When opening Point of Sale, you see the following error:
You have exceeded the maximum number of users who can access the company at one time
Intuit recommends the following 6 solutions for this problem. The first solution may solve your problem, or you may need to try all 6 to resolve the issue.
Close pos by clicking File > Exit instead of the X in upper right corner
If closing using the above method doesn't free up the licenses then Reboot all workstations. Although it may be inconvenient, it's an important step. Files can get stuck and the Point of Sale server can think too many workstations are open. If rebooting all workstations doesn't fix the issue, go to Solution 3.
If this solution does not resolve the issue, you can read discussions and post messages and questions relating to your issue on the QuickBooks Point of Sale Community Forum. You can also review other available support options for additional guidance.