I am getting this error.
Locating source for \'C:\\Users\\cem\\Documents\\Visual Studio 2008\\Projects\\CS.Web.Controls\\WebCropImage\\CropImage.cs\'. Checks
If is an ASP.Net project, delete the temporary files. This cannot hurt. Any time a copy is made, the possibility exists that somehow it can get out of sync.
C:\Windows\Microsoft.NET\Framework\v4.0.30319\Temporary ASP.NET Files\
In my case, before I did that, I could not set any breakpoints. The error was giving the exact same path in both MD5 statements, and saying the checksum didn't match.
After I did that, it still told me the source version was different, but I choose to use it anyway, and I was able to step through the code and set breakpoints.
Go figure.
And one more thing: If you want to know where it's getting the pdb from actually, you can go into Debug, Windows, Modules, and find the dll in question, and see the path in the Symbol File column.