Remote Desktop Disconnection

I have recently began using a Sonicwall Global VPN Client to allow remote staff to use our internal applications. The firewall is a SOHO 3 and the server is a basic Win2K Server. The main software package used is an ACU-COBOL based package. The problem is that it regularly disconnects the clients for no apparent reason. Some days is happens once a day and other days it happens every few minutes. The error message the clients get is – REMOTE DESKTOP DISCONNECTED. The connection to the remote computer was broken. This may have been caused by a network error. Please try connecting to the remote computer again. I have ensured that they are using a low screen resolution but to no avail. Can anyone help with this?