Multiple VPN connection for RB333

Dear All,
I have an RB333 router and configured via winbox, I seem to have an issue with multiple users connecting to a vpn on the internal network. The router is only allowing one vpn connection to be established from the internet network and doesnot work if multiple vpn connections are initiated from two different workstations. Is there any way to allow this ?

What kind of VPN?

thanks It’s PPTP