where can i set the number of concurrent nx users?

[Tomoki Taniguchi]

I have installed the NoMachine's version of NXserver.

I am currently finding that if one user has a nx session running I
can't get another user connected. I get "Reached the maximum number of
allowed users on this server"

what do i need to do to allow multiple simultaneous user sessions?

is this a limitation imposed on the "free" linux server?