LINQ to SQL Designer Bug

The *.designer.cs files are completely generated by designer. You should not write any your own code into this file. The classes and/or methods are partial, so you can extend/change the behaviour in the separate file.

Move using directives in your DataContext.cs and DataContext.designer.cs files into the namespace scope.

Don't place your own code in the designer file, instead use a separate file leveraging the partial classes concept.