When running AcuConnect Thin Client on a Windows Server sometimes the number of client connections is limited to say 26 even though the license allows significantly more users. The 27th attempt will receive an error "connection refused".
The Windows Desktop Heap configuration on the server is probably limiting the number of connections.
Here is the link to the Microsoft article with the info on Desktop Heap:
The pertinent information is under "Cause 2".
The Heap management is complex and some customers have resolved the issue by increasing one parameter while others decreased another parameter. Testing different settings will be required.
Remember to make a backup of the registry prior to making any changes.