'Class' does not contain a definition for 'Method'
There are three possibilities:
1) If you are referring old DLL then it cant be used. So you have refer new DLL
2) If you are using it in different namespace and trying to use the other namespace's dll then it wont refer this method.
3) You may need to rebuild the project
I think third option might be the cause for you. Please post more information in order to understand exact problem of yours.