iTalc problem the computers getting blocked

[TechMate]

Hello folks

 

I am new to the iTalc system, but I successfully installed it on two classes with one host and 5 clients.

It worked fine for more than an hour, than one ore more clients became blocked.

 

The screen on the blocked computer is getting black and slowly showing one square after the other.

 

I have had it running fine several times, after a while the problem starts.

 

I have made exceptions in the firewalls on all computers, but so far I have not done any similar thing with the anti virus or anti malware. Should I do that?

 

Which are the most probable causes? Any suggestion is appreciated.

 

Best regards TechMate