When trying to attach to process in Windows 2008 R2 64 bit you may get breakpoints that say they do not have symbols or cannot load symbols. I found a forum article where someone lists the fix:
By the way, for anyone else finding this article based on the same error message (at least in my case) was to modify the app pool in IIS. Go to advanced settings, change "Enable 32-Bit Applications" to True. VS2010, Win 7 64 bit.
You can check out the actual forum post at :http://stackoverflow.com/questions/708323/visual-studio-2008-with-asp-net-3-5-debuging-using-attach-to-process-is-not-work