Visual Studio 2012 It's not declared. It may be inaccessible due to its protection level

Hello guys.

I'm facing a problem with Visual Studio 2012 and watch window when debugging my application.

When debugging my application, using attach to process I'm unable to see variable values in watch Window, when I try to watch a variable it says  "<variablename> Its not declared. It may be inaccessible due to its protection level".

My application was migrated from Visual Studio 2005 to VS2012 but I still use .NET 2.0 due to some restrictions.

This error happens to some methods on my solution and I can't watch local variables only.

Thanks.