Applies To:
  • CitectSCADA 1.x 2.x 3.x 3.4

If you shutdown Citect while Citect is trying to call to a Citect server you may crash Windows for Workgroups to the DOS prompt. This is a bug in Windows for Workgoups 3.11. This problem does not occur with Windows 95 or Windows NT. 

On shutdown Citect will cancel any pending calls to Citect servers. When Citect tries to cancel a NetBIOS call under Windows for Workgroups, the call will not actually be cancelled, even though the cancel command completed successfully. This result is that the NetBIOS call will complete after Citect has shutdown and will cause Windows to crash out to the DOS prompt or hang. This is a bug in Windows for Workgoups 3.11.

If all your Citect servers are running correctly then this is not likely to occur, as all calls will complete very quickly. If your Citect servers are shutdown and you start up a Citect Client, the client will try to call the server once every 30 seconds and the call will timeout in a few seconds. So there is only a few second window in which if you shutdown you will see this problem. There for the chance of seeing this problem is about 1 in 15 shutdowns of Citect.

Citect version 3.4 and later checks for this error condition and will wait for all the pending NetBIOS calls to timeout before shutting down Citect. If the pending call does not complete after a long period of time Citect will display the error message "NCB did not cancel".