Are you using a VPN connection? What type of wire connection (T1, DSL, SDN,etc.)is being used? Is this a shared connection among the work stations or does each one have it’s own line?
If you are using a VPN over an open shared line (such as DSL)and a device is also using the same line without the VPN, then the server would detect this as a security problem and disconnect.
For example, if work station A is connected through the VPN via DSL and work station B has not connected to the VPN but accesses the internet, then the server would close the VPN connection. This would also happen if the phone system uses the same line – when someone makes a phone call the server closes the VPN.
I hope this helps.