VPN with L2tp/IPsec Problem

dear rextended

thanks for your time to answer about my question.

now my l2tp/ipsec is up and running.
the problem is i can’t connect to mikrotik VPN Server with different username even i already set different username for every PC that connect to the Mikrotik VPN server.

is always only one username that can connect, if i try connect with different username and PC, the one that already connect will disconnect.

any one can help me?
thankyou