Can't break vb.NET operation in VS 2010 -- no source loaded

I am using VS2010 to write ArcMap add-ins in vb.NET. 2008 worked fine but I switched to 2010 when I installed Arc 10.1. 2010 is working well except for debugging.

I can't assign break points or pause the add-in while it's running. I get messages that the source or symbols are not loaded. I have read about these issues on the MicroSoft web pages and changed the paths to DLLs and such in the debug > options section of VS 2010, but nothing works.

Has anyone else run into this and know how to fix it?

Thanks,
Derek