dropping terminal services connections via VPN

I’m having trouble with a remote site dropping connection to Win2k3 Server in an inconsistent manner. I have my VPNs running through a Sonic Wall TZ-170 and I’m making my terminal connection or Remote Desktop connection via the tunnel. When the connection is lost, I have to re-login, but it takes me back where I left, but I never loose my tunnel connection.

Need an expert, please; for I’m in the middle of this new project of remote connections for 10 companies nad this is just the foundation.