Windows 2008 R2 TS VPN connection closed when another user logs in

Hi.

I have a W 2008 R2 Ent. server with TS

I have VPN on the TS configured with a L2TP/Ipsec connection to connect to a customer site

Users will remote into the server, and make a VPN connection (click on shortcut to start VPN) and access the customer's site. This has worked OK for 2 years often with several users logged into the TS via RDP.

Recently users are encountering this problem: User A logs into the TS, makes VPN connection, accesses customer site. User B logs into the TS, user A's VPN connection is broken immediately. It seems to happen every time - not sporadic.

Can I get some suggestions on how to troubleshoot this?

Thanks!