I've been working a lot with stored procedures and the Linq to Sql designer. One of the annoyances is that all of a sudden when you drop the nth sproc to the designer it would not allow creating the codebehind anymore. It'll then throw the most usefull message:

"The operation could not be completed"

There's an easy fix however, open a Visual Studio command prompt and hit

"devenv /resetskippkg"

Works like a charm.