Most recently, I decided to reopen and resume a project which ran just fine on the same computer, about a month ago. in the interim, I had decided clean up all the temp files and cache and so on.
Now, when I ran the build, no errors. However, when I tried to run the project locally, visual studio would get stuck at 'loading symbol mscorlib.dll' and not budge. it seems to get frozen if I try to cancel, but not if i just let it be. no other activity on visual studio to see what is happening.
Still, no go.
Ultimately, I decided to just let visual studio load for as long as it takes.
After about 20 minutes, it seems to have obtained all the symbols.
Now, successive runs are happening within seconds. So, 'waiting' is simply the solution.