Upgrade My Code .net 2.0 to 4.0

Question

I have upgrade my code 2.0 to 4.0(vs2005 to vs2010).it showing following Error message.I Am using IBatis Framework

"BC30560: 'ExtensionAttribute' is ambiguous in the namespace 'System.Runtime.CompilerServices'."

Vulpes · Answer

The System.Runtime.CompilerServices.ExtensionAttribute class wasn't introduced until .NET 3.5 and is used to add extension methods in VB.NET which unlike C# lacks special syntax for this purpose. As they hadn't been introduced in .NET 2.0 you couldn't have used extension methods in your existing project though if you plan to alter it then you may want to use them in the future. The error message suggests that there's already an ExtensionAttribute being used in your project - perhaps something to do with the IBatis framework which I know nothing about. I suggest you try to track down all existing references to this attribute (which may be shortened to just Extension) figure out what namespace they're in and then replace them with a fully qualified reference i.e. namespace.Extension. That should then resolve the ambiguity.