By default, if the Web Transfer Client (WTC) sits idle for 5 minutes, the session is released so that others can use one of the concurrent licenses. You may want the session time to be longer or shorter, depending upon your user's expected usage.
You can control this with a Windows registry setting by creating a new DWORD value that specifies the number of minutes that you want the WTC session to be active, but idle, before the session is released.
HKEY_LOCAL_MACHINE\Software\GlobalSCAPE Inc.\EFT Server 3.0\WTCTimeout
Set the DWORD value to the number of minutes that a WTC session can remain idle before it is released for use by others. The default value is 5 minutes.
For more details of WTC-related registry settings, refer to Q10411 - HOWTO: Windows Registry Settings in the GlobalSCAPE Knowledge Base.