I'd suggest opening a Support case with the Integrity support folks, as there can be a few things that can lead to your users getting this error, around the licensing.
Here's a knowledge article that touches on some of these:
I've most often seen this issue, when seat licenses are used, and the group membership of those seat license groups become over-allocated (ex. more members in the appropriate license groups, than there are licenses). But again, there are a few things that can cause this.
What version of Integrity are you using, as that could also matter.