Here's the answer of my colleague Todor. If it doesn't help you to resolve this issue, please address it to the QSAR Toolbox Helpdesk
The Toolbox Server logs all errors and sends them to every new client that connects to it. In this way it informs all users about possible problems with module configuration.
In your case, the error message that you get means that a client, unknown to the server, is trying to access it. This can happen if you have previously closed a server while there was an active client which later tries to communicate with a newly started server. It is also possible that another client (on another machine or run by a different user) is trying to access your server.
Please close all Toolbox instances and then start the Toolbox Server manually. Does it report any errors while you still haven't started the Client? If yes, then there is a Toolbox Client running somewhere attempting to conenct to this Toolbox Server instance.
I'll pass this on to our IT people, since we have a central Toolbox server installation. Just out of curiosity: I can understand that an administrator would like to see this error message, but why would I - as a normal TB user - care about whether other users are known to the system or not?
Thanks again and have a nice weekend!