Exchange 2000 connection problems

I have VPN connectivity in the network with windows 2000 server and exchange 2000 server installed locally. The web domain is in the other locaton. It is connected thru. Adsl lines. The problem is when the user is in the local network open the ms outlook it shows an error message( when the wan link is not available)?network connection Is not available? Even the users are not able to see their mails , in the local server. In the outlook server configuration I have given local server address. After this error message the users have to close the outlook and re-open it then only they can access the mails. .

Kindly let me know how to solve this probs?