title: Missing reference to Microsoft.scripting.ExtensionAttrribute.dll
body: <p>We intermittently get this error on our .net 4 web forms web site. Recycling the app pool seems typically resolves it.</p>
  
  <p>The only references i can find to it seem to be related to either using <strong>Umbraco</strong>, or the Dynamic language Runtime. Neither of which applies to us. </p>
  
  <p>The only useful link I have found is this: <code>http://support.frozenmountain.com/entries/23667761-Compatibility-issue-using-ASP-Net-4-0-Extensions-and-ScriptManager</code></p>
  
  <p>Any other solutions, other than adding the unnecesary reference?   </p>
  
  <pre><code>System.Web.HttpUnhandledException (0x80004005): Exception of type   'System.Web.HttpUnhandledException' was thrown. ---&gt;   System.IO.FileNotFoundException: Could not load file or assembly 'Microsoft.Scripting.ExtensionAttribute,   Version=2.0.0.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies.   The system cannot find the file specified.  File name: 'Microsoft.Scripting.ExtensionAttribute, Version=2.0.0.0, Culture=neutral, PublicKeyToken=null'     at System.ModuleHandle.ResolveType(RuntimeModule module, Int32 typeToken, IntPtr* typeInstArgs, Int32 typeInstCount, IntPtr* methodInstArgs,   Int32 methodInstCount, ObjectHandleOnStack type)     at System.ModuleHandle.ResolveTypeHandleInternal(RuntimeModule module, Int32 typeToken, RuntimeTypeHandle[] typeInstantiationContext, RuntimeTypeHandle[] methodInstantiationContext)     at System.ModuleHandle.ResolveTypeHandle(Int32 typeToken, RuntimeTypeHandle[] typeInstantiationContext, RuntimeTypeHandle[] methodInstantiationContext)     at System.Reflection.RuntimeModule.ResolveType(Int32 metadataToken, Type[] genericTypeArguments, Type[] genericMethodArguments)     at System.Reflection.CustomAttribute.FilterCustomAttributeRecord(CustomAttributeRecord caRecord, MetadataImport scope, Assembly&amp; lastAptcaOkAssembly, RuntimeModule decoratedModule, MetadataToken decoratedToken, RuntimeType attributeFilterType, Boolean mustBeInheritable, Object[] attributes, IList derivedAttributes, RuntimeType&amp; attributeType, IRuntimeMethodInfo&amp; ctor, Boolean&amp; ctorHasParameters, Boolean&amp; isVarArg)     at System.Reflection.CustomAttribute.GetCustomAttributes(RuntimeModule decoratedModule, Int32 decoratedMetadataToken, Int32 pcaCount, RuntimeType attributeFilterType, Boolean mustBeInheritable, IList derivedAttributes, Boolean isDecoratedTargetSecurityTransparent)     at System.Reflection.CustomAttribute.GetCustomAttributes(RuntimeModule decoratedModule, Int32 decoratedMetadataToken, Int32 pcaCount, RuntimeType attributeFilterType, Boolean isDecoratedTargetSecurityTransparent)     at System.Reflection.CustomAttribute.GetCustomAttributes(RuntimeAssembly assembly, RuntimeType caType)     at System.Web.UI.AssemblyCache.GetAjaxFrameworkAssemblyAttribute(Assembly assembly)     at System.Web.UI.ScriptManager.get_DefaultAjaxFrameworkAssembly()     at System.Web.UI.ScriptManager..ctor()     at ASP.masterpages_safarinow_master.__BuildControlMasterScriptManager()     at ASP.masterpages_safarinow_master.__BuildControlfrmMain()     at ASP.masterpages_safarinow_master.__BuildControlmasterBodyTag()     at ASP.masterpages_safarinow_master.__BuildControlTree(masterpages_safarinow_master __ctrl)     at System.Web.UI.MasterPage.CreateMaster(TemplateControl owner, HttpContext context, VirtualPath masterPageFile, IDictionary contentTemplateCollection)     at System.Web.UI.Page.ApplyMasterPage()     at System.Web.UI.Page.PerformPreInit()     at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)    WRN: Assembly binding logging is turned OFF.  To enable assembly bind failure logging, set the registry value [HKLM\Software\Microsoft\Fusion!EnableLog] (DWORD) to 1.  Note: There is some performance penalty associated with assembly bind failure logging.  To turn this feature off, remove the registry value [HKLM\Software\Microsoft\Fusion!EnableLog].       at System.Web.UI.Page.HandleError(Exception e)     at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)     at System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)     at System.Web.UI.Page.ProcessRequest()     at System.Web.UI.Page.ProcessRequest(HttpContext context)     at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()     at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean&amp; completedSynchronously)
  </code></pre>