File Not Found on NewDwp.aspx in SharePoint when adding a web part

Do u receive this error and wandering what the hell is wrong with your portal:

File Not Found. at System.Signature._GetSignature(SignatureStruct& signature, Void* pCorSig, Int32 cCorSig, IntPtr fieldHandle, IntPtr methodHandle, IntPtr declaringTypeHandle) at System.Signature.GetSignature(SignatureStruct& signature, Void* pCorSig, Int32 cCorSig, RuntimeFieldHandle fieldHandle, RuntimeMethodHandle methodHandle, RuntimeTypeHandle declaringTypeHandle) at System.Signature..ctor(RuntimeMethodHandle methodHandle, RuntimeTypeHandle declaringTypeHandle) at System.Reflection.RuntimeMethodInfo.get_Signature() at System.Reflection.RuntimeMethodInfo.GetParameters() at Microsoft.SharePoint.WebPartPages.SPWebPartSerializer.GetPersonalizableProperties() at Microsoft.SharePoint.WebPartPages.SPWebPartManager.GetEffectiveWebPartType(Type webPartType, SerializationTarget serializationTarget, Boolean ignoreSupportsAttributeMarkup) at Microsoft.SharePoint.WebPartPages.SPWebPartManager.GetEffectiveWebPartType(Type aspWebPartType, SerializationTarget serializationTarget) at Microsoft.SharePoint.ApplicationPages.NewDwp.Page_PreRender(Object sender, EventArgs e) at System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e) at System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e) at System.Web.UI.Control.OnPreRender(EventArgs e) at Microsoft.SharePoint.WebControls.UnsecuredLayoutsPageBase.OnPreRender(EventArgs e) at System.Web.UI.Control.PreRenderRecursiveInternal() at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)


Problem is due to 2 factors:
1) You might have installed Smart Part web part in your server
2)and you don't have installed the ASP.NET AJAX installed in your server

To correct install the ASP.NET Ajax extension 1.0 from Microsoft Site

Restart server and you might get some relief.Do leave a message if it helps , helps me to understand how many got stuck in my situation :)

Article by david helped me ...

I loved this MOSS Posters!!!

http://technet.microsoft.com/en-us/office/bb310619.aspx