Firewall

We have several clients using one application on their Laptop to connect to Sql Server using either the dial-up or vpn client on their machine.Each client is behind the firewall.The query timeout on the sql server has been set to 0. Six out of 10 cases the application works fine,but when you let some screen open on the client's machine without any activity for may be 5 minutes(the application screen using sql server),come back and try to save the changes made by you and It's giving us the "Connection failure Error".
The same thing is not happeing over the LAN.

Any help in this matter is greatly appriciated.Can you modify the application to support disconnected recordsets and just update the changes as a batch ? Does it timeout on all of the machines outside of the firewall after the 5 minute mark ? Are you using connection pooling ?|||What is generating the error "Connection Failure" ? Is this the exact error message ?|||[DBNETLIB][ConnectionRead (recv()).]General network error. Check your network documentation.|||Are you able to access anything else behind the firewall - or do you lose all network access to the network behind the firewall ?|||Last time we were checking the connection behaviour in the Sql Server 2000 by using the sp_who command line and after some time(may be 6-8 minutes)we realized that there are no active connections between the Client and the Server.We think that the firewall is disconnecting the client with no activity after 10 minutes.Still searching|||We are using the CISCO firewall