[FreeNX-kNX] get 'Reached the maximum number of allowed users on this server' on newly created linux accounts when trying to connect

[Maccy]

Hi,

I'm experiencing a very strange problem whereby newly created users are 
not able to connect to a machine via NX but users that have been 
registered on my systems for a while can log in no problem.

They get the message 'Reached the maximum number of allowed users on 
this server' even though no-one else is logged on!

There is no known difference between the newly-created linux accounts - 
we're using Scientific Linux 4.3 (RHEL clone) - and the experienced user 
accounts.

I've tried....

a) Removing the key in .ssh/known_hosts on the client
b) Removing the .nx directory from both client and on the server
c) Rebooting and reinstalling the server
d) Recopying server SSH keys
e) Multiple clients and servers

I've even tried copying the entire contents of an experienced user's 
home directory over to the new accounts.

We're currently using the free version of the server from nomachine.com 
whilst we wait for unlimited licence keys.

Does anyone have any further suggestions?

Many thanks in advance,

Mark