We encountered a little problem that had us concerned until we figured out what was going on.
We had been running low on our seat count for licenses of SketchUp. We use a network license scheme that allows multiple people to share licenses as needed. Over the last few days we were running low on licenses and some were getting locked out. When we checked on it, several people were running multiple copies at one time.
We found that if you double click on a SketchUp file it open a new instance of SketchUp and takes up one license. Double click on another SketchUp file and another license gets checked out. We had several doing this and running multiple copies of SketchUp on the same machine. They had no idea they were doing it, but it was right there in their system tray. 3-4-5 seats of SketchUp running on the same machine.
Once we figured this out, we were okay again.
Sometimes it is the simplest things that catch you short handed.