I got this when selecting project properties at the first available opportunity after loading the solution. VAX was rescanning the headers at the time.
We press "Rebuild" in our options dialog then restart and open a project. Naturally, we do not get the error upon opening project properties while reparsing continues. Perhaps it depends on the current pane in the properties dialog. More likely, it's a timing issue.
We'll look through our code to see if something obvious jumps out.
Oops -- just noticed this post I'd forgotten about. Please don't fret ;) -- it was more an FYI than anything, as it had never happened before, and it hasn't happened since.