Hi Myrtha,
We haven't seen this problem with our SAPGUI 7.30 installations. There could be many things responsible, and it may not have anything to do with SAPGUI itself. To troubleshoot this you're going to need more information. I suggest you turn on tracing with one or more users where it has been happening and see if you can capture some information that might help analyze the problem.
Open up the SAP Logon Options:
Then go into Traces... SAP GUI Traces and activate Level 1: Errors. Do the same in SAP Logon Traces: activate Errors. Also click the button Delete All Trace Files to make sure you are starting fresh and won't be confusing old trace files. If you click Open Trace Folder you'll see where on the computer the traces will be stored. It's usually in %LOCALAPPDATA%\SAP\SAP GUI\Traces (or, C:\Users\<username>\AppData\Local\SAP\SAP GUI\Traces for a Win7 machine).
Once you've had it happen to a workstation with tracing enabled, hopefully that will provide more clues about what is going wrong.
Regards,
Matt