If a NULL pointer variable is requested from a control engine strategy by a PAC Display project or an OPC client, a recoverable error, a Stack Overflow error, may occur.
From PAC Control, if the Debugger is open at the time the Stack Overflow error occurs, a "Stack Full" error message appears. Select the Retry button to resume normal operation. If Debugger is not open at the time the error occurs, no other indication of a problem may be apparent.
From a PAC Display project, the Event Log may log that a tag or a group of tag qualities changed to "Bad Quality." At the Opto OPC Scanner level, a "Bad Quality" message may appear for the group of data that caused the Stack Overflow error.
After the Stack Overflow error occurs, the control engine stack is cleared, and the control engine resumes normal operation.
The firmware command used when a PAC Display project or Opto OPC Server client needs a value from the control engine, leaves an item on the control engine stack after accessing a NULL pointer variable.
Opto 22 has resolved this issue.