We have 10 licenses for Google SketchUp in my local office. We store the license file on a network drive that is accessible to all users. We've been finding that, at most, only 3 or 4 people can run it at one time before the license shows up as "expired" on another user's system. I've verified with Google that we have 10 licenses, and have downloaded updated license files from them.
The only thing that I can think of is that sometimes SketchUp crashes. Could this be utilizing a license somehow without giving it up? Google has not been able to answer this question.