Remote Assistance Error message

Remote Assistance Error message

For the last two weeks I ahve been unable to conenct to customers computers. They downlaod the custome rplugin and I give them the number code but they get "Win error, system.net web exception.
It has happended to 4 different customers. On each occassion I have tried a Remote assistance package from a difefrent venodr which logs in without a problem, so I am a bit puzzled by this. I ahve purchased a monthly licence and not running the free version.
Perhaps you can help
Thanks