If you encounter problems compiling your WebSharper project after an update of your dotnet installation, you might have to restart the service wsfscservice. Under linux you can simply issue the command pkill wsfscservice.

wsfscservice is used to speed up repeated compilation. As explained by Jand42:it uses AssemblyLoadContext for WS macros/offline site generator, but F# compiler part can sadly lock some dlls for TPs and it seems SDK update messes with it too.

In my case, after an upgrade from dotnet 6.0.405 to 6.0.406, I couldn’t compile the project and got pages of errors of this kind:

System.Reflection.ReflectionTypeLoadException: Unable to load one or more of
the requested types.Could not load file or assembly
'Microsoft.Extensions.Identity.Core, Version=6.0.0.0, Culture=neutral,
PublicKeyToken=adb9793829ddae60'. Reference assemblies should not be loaded for
execution.  They can only be loaded in the Reflection-only loader context.
(0x80131058)Could not load file or assembly
'Microsoft.Extensions.Identity.Stores, Version=6.0.0.0, Culture=neutral,
PublicKeyToken=adb9793829ddae60'. Reference assemblies should not be loaded for
execution.  They can only be loaded in the Reflection-only loader context.
(0x80131058)Could not load file or assembly
'Microsoft.Extensions.Identity.Core, Version=6.0.0.0, Culture=neutral,
PublicKeyToken=adb9793829ddae60'. Reference assemblies should not be loaded for
execution.  They can only be loaded in the Reflection-only loader context.
(0x80131058)Could not load file or assembly
'Microsoft.Extensions.Identity.Stores, Version=6.0.0.0, Culture=neutral,
PublicKeyToken=adb9793829ddae60'. Reference assemblies should not be loaded for
execution.  They can only be loaded in the Reflection-only loader context.
(0x80131058)Could not load file or assembly
'Microsoft.Extensions.Identity.Stores, Version=6.0.0.0, Culture=neutral,
PublicKeyToken=adb9793829ddae60'. Reference assemblies should not be loaded for
execution.  They can only be loaded in the Reflection-only loader context.
(0x80131058)Could not load file or assembly
'Microsoft.Extensions.Identity.Stores, Version=6.0.0.0, Culture=neutral,
PublicKeyToken=adb9793829ddae60'. Reference assemblies should not be loaded for
execution.  They can only be loaded in the Reflection-only loader context.
(0x80131058)Could not load file or assembly
'Microsoft.Extensions.Identity.Core, Version=6.0.0.0, Culture=neutral,
PublicKeyToken=adb9793829ddae60'. Reference assemblies should not be loaded for
execution.  They can only be loaded in the Reflection-only loader context.
(0x80131058)Could not load file or assembly
'Microsoft.Extensions.Identity.Core, Version=6.0.0.0, Culture=neutral,
PublicKeyToken=adb9793829ddae60'. Reference assemblies should not be loaded for
execution.  They can only be loaded in the Reflection-only loader context.
(0x80131058)Could not load file or assembly
'Microsoft.Extensions.Identity.Core, Version=6.0.0.0, Culture=neutral,
PublicKeyToken=adb9793829ddae60'. Reference assemblies should not be loaded for
execution.  They can only be loaded in the Reflection-only loader context.
(0x80131058)Could not load file or assembly
'Microsoft.Extensions.Identity.Stores, Version=6.0.0.0, Culture=neutral,
PublicKeyToken=adb9793829ddae60'. Reference assemblies should not be loaded for
execution.  They can only be loaded in the Reflection-only loader context.
(0x80131058)Could not load file or assembly
'Microsoft.Extensions.Identity.Stores, Version=6.0.0.0, Culture=neutral,
PublicKeyToken=adb9793829ddae60'. Reference assemblies should not be loaded for
execution.  They can only be loaded in the Reflection-only loader context.
(0x80131058)Could not load file or assembly
'Microsoft.Extensions.Identity.Core, Version=6.0.0.0, Culture=neutral,
PublicKeyToken=adb9793829ddae60'. Reference assemblies should not be loaded for
execution.  They can only be loaded in the Reflection-only loader context.  at
System.Reflection.RuntimeModule.GetTypes(RuntimeModule module)   at
System.Reflection.RuntimeAssembly.get_DefinedTypes()   at
WebSharper.Compiler.FSharp.CodeReader.SymbolReader.ResolveAnonRecord(FSharpAnonRecordTypeDetails
d)   at WebSharper.Compiler.FSharp.CodeReader.SymbolReader.ReadTypeSt(Boolean
markStaticTP, FSharpMap`2 tparams, FSharpType t)   at
WebSharper.Compiler.FSharp.CodeReader.SymbolReader.ReadType(FSharpMap`2
tparams, FSharpType t)   at
WebSharper.Compiler.FSharp.CodeReader.SymbolReader.ReadMember(FSharpMemberOrFunctionOrValue
x, FSharpOption`1 cls)   at
WebSharper.Compiler.FSharp.ProjectReader.getAnnot@278(SymbolReader sr,
FSharpEntity cls, TypeAnnotation annot, Dictionary`2 annotations,
FSharpMemberOrFunctionOrValue x)   at
WebSharper.Compiler.FSharp.ProjectReader.transformClass(Lazy`1 sc, Compilation
comp, ResolveFuncArgs ac, SymbolReader sr, Dictionary`2 classAnnots,
FSharpFunc`2 isInterface, Dictionary`2 recMembers, FSharpEntity cls, List`1
members)   at
WebSharper.Compiler.FSharp.ProjectReader.transformAssembly@1308-2.Invoke(FSharpImplementationFileContents
file)   at Microsoft.FSharp.Collections.SeqModule.Iterate[T](FSharpFunc`2
action, IEnumerable`1 source) in D:\a\_work\1\s\src\FSharp.Core\seq.fs:line 603
at WebSharper.Compiler.FSharp.ProjectReader.transformAssembly(LoggerBase
logger, Compilation comp, String assemblyName, WsConfig config,
FSharpCheckProjectResults checkResults)   at
WebSharper.Compiler.FSharp.WebSharperFSharpCompiler.Compile(Task`1 prevMeta,
String[] argv, WsConfig config, String assemblyName, FSharpOption`1 logger)
at WebSharper.Compiler.FSharp.Compile.comp@191.Invoke(Unit unitVar0)   at
WebSharper.Compiler.AssemblyResolver.Wrap[T](FSharpFunc`2 action)   at
WebSharper.Compiler.FSharp.Compile.Compile$cont@136-1(WsConfig config,
WarnSettings warnSettings, LoggerBase logger, FSharpFunc`2 tryGetMetadata,
String thisName, FSharpChecker checker, Boolean isBundleOnly, String[]
jsCompilerArgs, Unit unitVar)   at
WebSharper.Compiler.FSharp.Compile.Compile$cont@100(WsConfig config,
WarnSettings warnSettings, LoggerBase logger, FSharpFunc`2 checkerFactory,
FSharpFunc`2 tryGetMetadata, String thisName, Unit unitVar)   at
WebSharper.Compiler.FSharp.Compile.Compile(WsConfig config, WarnSettings
warnSettings, LoggerBase logger, FSharpFunc`2 checkerFactory, FSharpFunc`2
tryGetMetadata)   at
Program.compilationResultForDebugOrRelease@152(FSharpFunc`2 checkerFactory,
FSharpFunc`2 tryGetMetadata, LoggerBase logger, WsConfig wsConfig, WarnSettings
warnSettings, String[] args, Unit unitVar0)System.BadImageFormatException:
Could not load file or assembly 'Microsoft.Extensions.Identity.Core,
Version=6.0.0.0, Culture=neutral, PublicKeyToken=adb9793829ddae60'. Reference
assemblies should not be loaded for execution.  They can only be loaded in the
Reflection-only loader context. (0x80131058)File name:
'Microsoft.Extensions.Identity.Core, Version=6.0.0.0, Culture=neutral,
PublicKeyToken=adb9793829ddae60' ---> System.BadImageFormatException: Cannot
load a reference assembly for execution.System.BadImageFormatException: Could
not load file or assembly 'Microsoft.Extensions.Identity.Stores,
Version=6.0.0.0, Culture=neutral, PublicKeyToken=adb9793829ddae60'. Reference
assemblies should not be loaded for execution.  They can only be loaded in the
Reflection-only loader context. (0x80131058)File name:
'Microsoft.Extensions.Identity.Stores, Version=6.0.0.0, Culture=neutral,
PublicKeyToken=adb9793829ddae60' ---> System.BadImageFormatException: Cannot
load a reference assembly for execution.System.BadImageFormatException: Could
not load file or assembly 'Microsoft.Extensions.Identity.Core, Version=6.0.0.0,
Culture=neutral, PublicKeyToken=adb9793829ddae60'. Reference assemblies should
not be loaded for execution.  They can only be loaded in the Reflection-only
loader context. (0x80131058)File name: 'Microsoft.Extensions.Identity.Core,
Version=6.0.0.0, Culture=neutral, PublicKeyToken=adb9793829ddae60' --->
System.BadImageFormatException: Cannot load a reference assembly for
execution.System.BadImageFormatException: Could not load file or assembly
'Microsoft.Extensions.Identity.Stores, Version=6.0.0.0, Culture=neutral,
PublicKeyToken=adb9793829ddae60'. Reference assemblies should not be loaded for
execution.  They can only be loaded in the Reflection-only loader context.
(0x80131058)File name: 'Microsoft.Extensions.Identity.Stores, Version=6.0.0.0,
Culture=neutral, PublicKeyToken=adb9793829ddae60' --->
System.BadImageFormatException: Cannot load a reference assembly for
execution.System.BadImageFormatException: Could not load file or assembly
'Microsoft.Extensions.Identity.Stores, Version=6.0.0.0, Culture=neutral,
PublicKeyToken=adb9793829ddae60'. Reference assemblies should not be loaded for
execution.  They can only be loaded in the Reflection-only loader context.
(0x80131058)File name: 'Microsoft.Extensions.Identity.Stores, Version=6.0.0.0,
Culture=neutral, PublicKeyToken=adb9793829ddae60' --->
System.BadImageFormatException: Cannot load a reference assembly for
execution.System.BadImageFormatException: Could not load file or assembly
'Microsoft.Extensions.Identity.Stores, Version=6.0.0.0, Culture=neutral,
PublicKeyToken=adb9793829ddae60'. Reference assemblies should not be loaded for
execution.  They can only be loaded in the Reflection-only loader context.
(0x80131058)File name: 'Microsoft.Extensions.Identity.Stores, Version=6.0.0.0,
Culture=neutral, PublicKeyToken=adb9793829ddae60' --->
System.BadImageFormatException: Cannot load a reference assembly for
execution.System.BadImageFormatException: Could not load file or assembly
'Microsoft.Extensions.Identity.Core, Version=6.0.0.0, Culture=neutral,
PublicKeyToken=adb9793829ddae60'. Reference assemblies should not be loaded for
execution.  They can only be loaded in the Reflection-only loader context.
(0x80131058)File name: 'Microsoft.Extensions.Identity.Core, Version=6.0.0.0,
Culture=neutral, PublicKeyToken=adb9793829ddae60' --->
System.BadImageFormatException: Cannot load a reference assembly for
execution.System.BadImageFormatException: Could not load file or assembly
'Microsoft.Extensions.Identity.Core, Version=6.0.0.0, Culture=neutral,
PublicKeyToken=adb9793829ddae60'. Reference assemblies should not be loaded for
execution.  They can only be loaded in the Reflection-only loader context.
(0x80131058)File name: 'Microsoft.Extensions.Identity.Core, Version=6.0.0.0,
Culture=neutral, PublicKeyToken=adb9793829ddae60' --->
System.BadImageFormatException: Cannot load a reference assembly for
execution.System.BadImageFormatException: Could not load file or assembly
'Microsoft.Extensions.Identity.Core, Version=6.0.0.0, Culture=neutral,
PublicKeyToken=adb9793829ddae60'. Reference assemblies should not be loaded for
execution.  They can only be loaded in the Reflection-only loader context.
(0x80131058)File name: 'Microsoft.Extensions.Identity.Core, Version=6.0.0.0,
Culture=neutral, PublicKeyToken=adb9793829ddae60' --->
System.BadImageFormatException: Cannot load a reference assembly for
execution.System.BadImageFormatException: Could not load file or assembly ```