Visual Studio No Symbols have been loaded for this document

I am having some trouble debugging a visual studio 2008 C++ project. When I start running it in debug, the breakpoints are disabled with the message

The Breakpoint will not be hit. No Symbols have been loaded for this document.

I have tried cleaning and rebuilding, but this doesn't make a difference.

I also tried looking in Debug->Windows->Modules. If I right click on the module I am trying to debug and press Symbol load information it brings up a list of places it has tried to load the symbols from. The first in the list is correct and the file exists, but next to it is this error

C:\path\to\my\symbol\Debug\MyProject.pdb: Unknown symbol handler for error

Does anyone know what causes this or how to fix it?

First of all, it is possible that some of your modules won't show in the module window, because some of them may be loaded dynamically (only as needed).

You might want to check in your project properties under Linker > Debugging > Generate Program Database File and Generate Debug Info. Be sure these two are set properly.

Also, check if C/C++ > General > Debug Information Format is set to Program Database for Edit And Continue (/ZI) or something similar.

I know you mentioned that your symbol file exists, but checking what I just mentioned will ensure you have the right version of your symbol in the right place.

Finally, check if all your project and files in your solution are set to compile as Debug and not Release or something else, because no symbols will be generated (hence none will be loaded) for this project / file.

Hope this helps a bit.

In my case, the problem was solved by checking "Use Managed Compatibility Mode" in Tools / Options / Debugging / General.

In case anyone has this problem when using 'Attach to process', the answer to this question solved it for me:

Visual Studio is not loading modules when attaching to process

Specifically, switching to 'Native code' in the 'Attach to' options instead of 'Auto'.

I have managed to solve this by copying my source sideways and checking out a completely clean copy. I assume it was some setting stored in the projects .suo file.