Canot debug clickonce app

I have a  .NET app that used to work. Now I stumble upon this very annoying problem. I cannot debug.

---------------------------
                Microsoft Visual Studio
                ---------------------------
                The following module was built either with optimizations enabled or without debug information:

                C:\[....].DLL

                To debug this module, change its project build configuration to Debug mode. To suppress this message, disable the 'Warn if no user code on launch' debugger option.
                ---------------------------
                OK  
                ---------------------------

I've seen the proposed solution here, but this just suppress the error message.

VisualStudio 2008

Any ideas ?