Nope, no VSS here.  (tried it for a while but it was causing me headaches.
will probably check back in on it when 'VSS.Net' rolls around...)

For the first time today, I saw the problem the way Jeff described:  no
build errors at the moment that i clicked the 'debug' button, but by the
time it finished 'pre-build validation', there were phantom errors!  It
happened after I got done making some relatively big changes to a Crystal
Report.  Maybe the custom code-generation tool is interfering with
background compilation?

The interesting thing is (at least in my case), the errors are always the
same.  Strange because you'd think that as the project size changed, the
point at which VS.Net chokes would change also.  Maybe it's something about
a particular file.

...pure speculation.  no time to really try to diagnose these issues - i
have my own app's problems to fix! =)

good luck all! =)