This Breakpoint Will Not Currently Be Hit, The Source Code is Different from the Original (even after cleaning/rebuilding)

I've had this problem once myself but that was on a vsto addin. In that case there were left over intermediate files under the users/appdata directories that were actually loaded instead of my app.

There is this blog article that has a whole load of possible reasons for this error and then a whole bunch more in the comments from other users

This can also happen if you have a solution with multiple projects, and have the wrong project selected as your startup project in VS2010 and VS2012.

Now, obviously, I wouldn't expect debugging to work if I have the wrong startup project selected -- the debugger is attaching itself to the wrong process!

But this error message (in my case) was terribly misleading. It made me think something else was wrong. I tried a bunch of solutions in this thread (nuking various /bin and output directories) when really it was something very simple (wrong startup process).