error when using filehelpers on IIS; sometimes :S : [PolicyException: Required permissions cannot be acquired.]

FileHelpers.dll (2.0) are referenced within 2 class libraryies (Dto and Services) in my solution
My webapp (asp.net mvc) is on IIS7 (Full Trust) Windows 7 PRO 64 and I sometimes get this exception when starting my app from VS2008: (to get rid of it I delete the FileHelpers.dll from bin, run, close browser, rebuild the solution and run again )

     [PolicyException: Required permissions cannot be acquired.]
       System.Security.SecurityManager.ResolvePolicy(Evidence evidence, PermissionSet reqdPset, PermissionSet optPset, PermissionSet denyPset, PermissionSet& denied, Boolean checkExecutionPermission) +10238142
       System.Security.SecurityManager.ResolvePolicy(Evidence evidence, PermissionSet reqdPset, PermissionSet optPset, PermissionSet denyPset, PermissionSet& denied, Int32& securitySpecialFlags, Boolean checkExecutionPermission) +97

    [FileLoadException: Could not load file or assembly 'FileHelpers, Version=2.0.0.0, Culture=neutral, PublicKeyToken=3e0c08d59cc3d657' or one of its dependencies. Failed to grant minimum permission requests. (Exception from HRESULT: 0x80131417)]
       System.Reflection.Assembly._nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, Assembly locationHint, StackCrawlMark& stackMark, Boolean throwOnFileNotFound, Boolean forIntrospection) +0
       System.Reflection.Assembly.InternalLoad(AssemblyName assemblyRef, Evidence assemblySecurity, StackCrawlMark& stackMark, Boolean forIntrospection) +416
       System.Reflection.Assembly.InternalLoad(String assemblyString, Evidence assemblySecurity, StackCrawlMark& stackMark, Boolean forIntrospection) +166
       System.Reflection.Assembly.Load(String assemblyString) +35
       System.Web.Configuration.CompilationSection.LoadAssemblyHelper(String assemblyName, Boolean starDirective) +190

    [ConfigurationErrorsException: Could not load file or assembly 'FileHelpers, Version=2.0.0.0, Culture=neutral, PublicKeyToken=3e0c08d59cc3d657' or one of its dependencies. Failed to grant minimum permission requests. (Exception from HRESULT: 0x80131417)]
       System.Web.Configuration.CompilationSection.LoadAssemblyHelper(String assemblyName, Boolean starDirective) +11207304
       System.Web.Configuration.CompilationSection.LoadAllAssembliesFromAppDomainBinDirectory() +388
       System.Web.Configuration.CompilationSection.LoadAssembly(AssemblyInfo ai) +232
       System.Web.Configuration.AssemblyInfo.get_AssemblyInternal() +48
       System.Web.Compilation.BuildManager.GetReferencedAssemblies(CompilationSection compConfig) +210
       System.Web.Compilation.BuildProvidersCompiler..ctor(VirtualPath configPath, Boolean supportLocalization, String outputAssemblyName) +76
       System.Web.Compilation.ApplicationBuildProvider.GetGlobalAsaxBuildResult(Boolean isPrecompiledApp) +283
       System.Web.Compilation.BuildManager.CompileGlobalAsax() +50
       System.Web.Compilation.BuildManager.EnsureTopLevelFilesCompiled() +676

    [HttpException (0x80004005): Could not load file or assembly 'FileHelpers, Version=2.0.0.0, Culture=neutral, PublicKeyToken=3e0c08d59cc3d657' or one of its dependencies. Failed to grant minimum permission requests. (Exception from HRESULT: 0x80131417)]
       System.Web.Compilation.BuildManager.ReportTopLevelCompilationException() +76
       System.Web.Compilation.BuildManager.EnsureTopLevelFilesCompiled() +1012
       System.Web.Hosting.HostingEnvironment.Initialize(ApplicationManager appManager, IApplicationHost appHost, IConfigMapPathFactory configMapPathFactory, HostingEnvironmentParameters hostingParameters) +1025

[HttpException (0x80004005): Could not load file or assembly 'FileHelpers, Version=2.0.0.0, Culture=neutral, PublicKeyToken=3e0c08d59cc3d657' or one of its dependencies. Failed to grant minimum permission requests. (Exception from HRESULT: 0x80131417)]
   System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +11301302
   System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +88
   System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +4338644

I tried to switch to FileHelpers 1.6 which don't use reflection.emit and I get this exception:

    Stack Trace: 


[PolicyException: Required permissions cannot be acquired.]
   System.Security.SecurityManager.ResolvePolicy(Evidence evidence, PermissionSet reqdPset, PermissionSet optPset, PermissionSet denyPset, PermissionSet& denied, Boolean checkExecutionPermission) +10238142
   System.Security.SecurityManager.ResolvePolicy(Evidence evidence, PermissionSet reqdPset, PermissionSet optPset, PermissionSet denyPset, PermissionSet& denied, Int32& securitySpecialFlags, Boolean checkExecutionPermission) +97

[FileLoadException: Could not load file or assembly 'FileHelpers, Version=1.6.0.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. Failed to grant minimum permission requests. (Exception from HRESULT: 0x80131417)]
   System.Reflection.Assembly._nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, Assembly locationHint, StackCrawlMark& stackMark, Boolean throwOnFileNotFound, Boolean forIntrospection) +0
   System.Reflection.Assembly.InternalLoad(AssemblyName assemblyRef, Evidence assemblySecurity, StackCrawlMark& stackMark, Boolean forIntrospection) +416
   System.Reflection.Assembly.InternalLoad(String assemblyString, Evidence assemblySecurity, StackCrawlMark& stackMark, Boolean forIntrospection) +166
   System.Reflection.Assembly.Load(String assemblyString) +35
   System.Web.Configuration.CompilationSection.LoadAssemblyHelper(String assemblyName, Boolean starDirective) +190

[ConfigurationErrorsException: Could not load file or assembly 'FileHelpers, Version=1.6.0.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. Failed to grant minimum permission requests. (Exception from HRESULT: 0x80131417)]
   System.Web.Configuration.CompilationSection.LoadAssemblyHelper(String assemblyName, Boolean starDirective) +11207304
   System.Web.Configuration.CompilationSection.LoadAllAssembliesFromAppDomainBinDirectory() +388
   System.Web.Configuration.CompilationSection.LoadAssembly(AssemblyInfo ai) +232
   System.Web.Configuration.AssemblyInfo.get_AssemblyInternal() +48
   System.Web.Compilation.BuildManager.GetReferencedAssemblies(CompilationSection compConfig) +210
   System.Web.Compilation.BuildProvidersCompiler..ctor(VirtualPath configPath, Boolean supportLocalization, String outputAssemblyName) +76
   System.Web.Compilation.ApplicationBuildProvider.GetGlobalAsaxBuildResult(Boolean isPrecompiledApp) +283
   System.Web.Compilation.BuildManager.CompileGlobalAsax() +50
   System.Web.Compilation.BuildManager.EnsureTopLevelFilesCompiled() +676

[HttpException (0x80004005): Could not load file or assembly 'FileHelpers, Version=1.6.0.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. Failed to grant minimum permission requests. (Exception from HRESULT: 0x80131417)]
   System.Web.Compilation.BuildManager.ReportTopLevelCompilationException() +76
   System.Web.Compilation.BuildManager.EnsureTopLevelFilesCompiled() +1012
   System.Web.Hosting.HostingEnvironment.Initialize(ApplicationManager appManager, IApplicationHost appHost, IConfigMapPathFactory configMapPathFactory, HostingEnvironmentParameters hostingParameters) +1025

[HttpException (0x80004005): Could not load file or assembly 'FileHelpers, Version=1.6.0.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. Failed to grant minimum permission requests. (Exception from HRESULT: 0x80131417)]
   System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +11301302
   System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +88
   System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +4338644

Sort of a stab in the dark here, but try three things:

• In IIS manager, find the application pool that your application is running under and open up the advanced settings. Make sure the Enable 32 bit applicaitons" setting is true.

• Make sure you are running Visual Studio as an administrator.

• Check the references in solution explorer for your sub-projects. Try setting the "copy local" property on reference for the FileHelpers to false. You'll probably need to add a reference to this assembly directly in your web project, and there you'd leave copy local set to true. (I've seen cases where two sub-projects trying to push in the same referenced DLLs to a single web app can cause interesting side-effects). Also make sure both sub-projects reference the EXACT same FileHelpers assembly from the same physical location.