I was trying to debug a project we're maintaining just now and I kept getting "The breakpoint will not currently be hit. No symbols have been loaded for this document." after setting a breakpoint and running the solution. The Startup project is a Smart Device project targetting Windows Mobile 6.1 Standard and it was deploying to an emulator running the same.
After trying all of the suggestions from posts like this one including manually trying to point at the .pdb file, I then kept getting "The symbol file x does not match the module" where x was the name of the relevant .pdb file. Eventually I noticed a comment on that same post regarding deleting the actual .exe which has been deployed to the emulator and then redeploying which for some reason did the trick.