Strange IIS 10 error


Getting a strange IIS error (Windows 10 Professional, IIS 10) on my development PC from even a simple ASPX page:

<!DOCTYPE html>
<html lang="en" xmlns="">
    <meta charset="utf-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <title>Test Page</title>

Any ASPX page (including above) returns a 500 error with the following exception/stack trace:

[IOException: The file cannot be accessed by the system.
   System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath) +1143
   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) +1242
   System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share) +126
   Microsoft.CodeDom.Providers.DotNetCompilerPlatform.Compiler.get_CompilerName() +130
   Microsoft.CodeDom.Providers.DotNetCompilerPlatform.Compiler.FromFileBatch(CompilerParameters options, String[] fileNames) +826
   Microsoft.CodeDom.Providers.DotNetCompilerPlatform.Compiler.CompileAssemblyFromFileBatch(CompilerParameters options, String[] fileNames) +185
   System.Web.Compilation.AssemblyBuilder.Compile() +2032
   System.Web.Compilation.BuildProvidersCompiler.PerformBuild() +357
   System.Web.Compilation.ApplicationBuildProvider.GetGlobalAsaxBuildResult(Boolean isPrecompiledApp) +12029645
   System.Web.Compilation.BuildManager.CompileGlobalAsax() +52
   System.Web.Compilation.BuildManager.EnsureTopLevelFilesCompiled() +341

[HttpException (0x80004005): The file cannot be accessed by the system.
   System.Web.Compilation.BuildManager.ReportTopLevelCompilationException() +76
   System.Web.Compilation.BuildManager.EnsureTopLevelFilesCompiled() +631
   System.Web.Compilation.BuildManager.CallAppInitializeMethod() +38
   System.Web.Hosting.HostingEnvironment.Initialize(ApplicationManager appManager, IApplicationHost appHost, IConfigMapPathFactory configMapPathFactory, HostingEnvironmentParameters hostingParameters, PolicyLevel policyLevel, Exception appDomainCreationException) +758

[HttpException (0x80004005): The file cannot be accessed by the system.
   System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +552
   System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +122
   System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +737

The system used to work properly as of about 6 days ago: Only changes are the latest windows update (version 1903)--yeah haven't ruled that out.

Old .ASP pages load correctly and I've verified that the system is loading/accessing the ASPX config files (web.config, global.asax, etc.).

Also tried uninstalling/reinstalling IIS to no avail.

asked on Super User Jun 24, 2019 by Jamie

1 Answer


Found it! Sheesh: my IIS directory path is contained within dropbox and dropbox decided to smart sync some of the roslyn files out. Thus IIS couldn't access them since the names were merely placeholders.

answered on Super User Jun 24, 2019 by Jamie

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