Hi,
We did have similar problems with some of our users losing connection to PASS, but I don't have the exact details of the error messages. This issue was a network one, with a section of network the users were on becoming disconnected from the network, caused by a faulty internet cable. We replaced the cable which cured the problem.
Your problem sounds more like an issue at the server end with either the PASS losing network connection or the something happening on the server. We found that the interruption was intermittent but PASS was more susceptible to interruption. compared to applications like Outlook that were able to reconnect when PASS couldn't.
Hope this helps