Are you saying that you have multiple clients connecting from the same remote IP address?
If that is the case then, yes, you will have problems. Due to the way the traffic is encrypted it's difficult for the server to identify connection A from connection B, so the earlier sessions will disconnect. It does not matter whether they are using the same account or not, it's all based on their IP address.
There are three common solutions - the first is to run multiple VPN protocols. Mac OS X Server supports PPTP and L2TP. You can connect one client on each, even from the same IP address, and not run into problems.
If you have more than two clients from the same IP address then this won't work, of course. A solution here involves either configuring a site-to-site VPN (rather than a client-to-site VPN), so that every device on the remote network shares the same VPN connection.
The last option is to replace your router on the remote (client) end with one that supports multiple VPN tunnels via NAT-T - this extension allows multiple clients to maintain a VPN connection, but not all routers support it.