2 projects in solution vut can't debug one of them

Hi All
I have a Main project that usually imports a home crafted dll.
I have been adding to the dll a lot recently and decided it would be easier to debug if instead of referencing the dll in the Main project
I'd add the dll project back into the Main Solution.
Hope that is clear!

I removed the reference to the DLL and changed the reference to the new dll that is now in the Main debug folder .
I expected that I would now be able to step through the code in the dll project.
I can set a breakpoint but it never works and I can't single step into it either.

I tried removing any reference to the dll but then got hundreds of errors.

Obviously I'm missing something. I know I've done similar things before and it worked?
BTW I am creating a pdb file for the dll project!

Any help would be appreciated :wave:

Mike