Tally 7.2 gold-Multi user

Hi
I am tally 7.2 gold multi user.i got a problem of installed client.i ws using the same computers in through same network setting.but suddenly after few time i got problem in on client computers.it shows licinced serial no. on client computer.but on selecting companies to open.It shows error message written "Failed to Open Company ". i need support on how i can succesfully use tally gold multi user.on client.remember i was using bfor same computers.

Regards
Amirali Jamani