Albert,
I do not believe it has anything to do with the software version of your Cisco. It could be for many reasons. The first would be to find out which side of the call (Cisco or Quintum) is disconnecting the call and why. Without reviewing the log, there is no way I can tell. If you would like to have me assist you in troubleshooting this, please email me at mike_voip@hotmail.com.
Mike