CSC compiler error in Sitecore application

We have an issue where the editors in Sitecore experience trouble with change language in the Content Editor.

This happens because a compiled dll was not found.

Exception: System.IO.FileNotFoundException
Message: Could not find file 'C:\WINDOWS\TEMP\gwp5mkkl.dll'.
Source: mscorlib
at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
at System.IO.FileStream.Init(String path, FileMode mode, FileAccess 
access, Int32 rights, Boolean useRights, FileShare share, Int32 
bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String 
msgPath, Boolean bFromProxy, Boolean useLongPath, Boolean checkHost)
at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess 
access, FileShare share, Int32 bufferSize, FileOptions options, String 
msgPath, Boolean bFromProxy, Boolean useLongPath, Boolean checkHost)
at System.IO.File.InternalReadAllBytes(String path, Boolean checkHost)
at Microsoft.CSharp.CSharpCodeGenerator.FromFileBatch(CompilerParameters 
options, String[] fileNames)
at 
Microsoft.CSharp.CSharpCodeGenerator.FromSourceBatch(CompilerParameters 
options, String[] sources)
at Microsoft.CSharp.CSharpCodeGenerator.System.CodeDom.
Compiler.ICodeCompiler.CompileAssemblyFromSourceBatch(CompilerParameters 
options, String[] sources)
at Sitecore.CodeDom.Compiler.CSharpCompiler.Compile(String sourceFile, 
String code, String assemblyFile, StringCollection referencedAssemblies)
at Sitecore.CodeDom.Compiler.CSharpCompiler.Compile(String code, 
StringCollection referencedAssemblies)
at Sitecore.CodeDom.Compiler.CSharpCompiler.SourceToMemory(String code, 
StringCollection referencedAssemblies)
at Sitecore.Web.UI.XmlControls.FolderControlSource.
BuildControlAssembly(XmlNode fileNode, String& assemblyKey, String& 
assemblyFile)
at Sitecore.Web.UI.XmlControls.FolderControlSource.
GetControlAssembly(String controlName, String& assemblyKey)
at Sitecore.Web.UI.XmlControls.FolderControlSource.ResolveType(String 
controlName, Boolean includeDynamicTypes)
at Sitecore.Web.UI.XmlControls.ControlSource.GetControlType(String 
namespacePrefix, String controlName, String mode, Boolean 
includeDynamicTypes)
at Sitecore.Web.UI.XmlControls.ControlFactory.GetControlType(String 
controlName, String mode, Boolean includeDynamicTypes)
at Sitecore.Web.UI.XmlControls.ControlFactory.GetControl(Control parent, 
String controlName, String mode, Object[] properties, AllowGenericControl 
allowGeneric)
at Sitecore.Shell.DefaultPage.OnInit(EventArgs e)
at System.Web.UI.Control.InitRecursive(Control namingContainer)
at System.Web.UI.Page.ProcessRequestMain(Boolean 
includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

This occurs because the csc.exe fails to generate the dll file

Faulting application name: csc.exe, version: 4.6.1590.0, time stamp: 
0x5787f44f
Faulting module name: KERNELBASE.dll, version: 6.3.9600.17936, time 
stamp: 0x55a68e0c
Exception code: 0xc0000142
Fault offset: 0x00000000000ec4e0
Faulting process id: 0x3680
Faulting application start time: 0x01d37027490a9fd7
Faulting application path: 
C:\Windows\Microsoft.NET\Framework64\v4.0.30319\csc.exe
Faulting module path: KERNELBASE.dll
Report Id: 86b98dc0-dc1a-11e7-80f9-00155d003b30
Faulting package full name: 
Faulting package-relative application ID:

According to the Sitecore support this is an issue with the .NET and, therefore, they can't help to resolve the issue.

Have any of you guys experienced something like this?

We have tried reinstalling the .Net framework with no result.

This issue occurs periodically and when it does, it is necessary to restart the server. An IIS reset is not enough. It's not because of write access to the C:\temp folder. The application has the correct access and it does work for most of the time.

Any ideas?

Bit of a shot in the dark, but:

Is there some sort of background process running that locks or removes files in the Windows temp folder?

When you say Sitecore runs fine for a while but then will break with this error, that makes me think that something made the runtime-generated DLL you mention become unreadable. The most obvious explanations I can think of for that would be:

• "files get deleted from the temp folder" (maybe a process trying to free up disk space?)
• "the file becomes locked, and cannot be read by ASP.Net" (maybe an agressive backup or virus scanner process?)

Does the file referenced physically exist after the website has crashed? If so, can something like Process Explorer tell you what task(s) have locks against it? And if it really has disappeared, can you apply some auditing to log what goes on in the temp folder and see what processes create and remove this file?