In PAC Control or ioControl, if you Modify an existing controller name from Configure→Control Engines, Modify such that you change the first letter from upper case to lower case, or vice-versa, and click OK, the controller name disappears from the Select Control Engine dialog. However, the control engine name remains listed in the Configure Control Engines dialog.
Control Engine name: Io31Din
Changed to: io31Din
The above name change causes the control engine name to disappear from the Select Control Engine list.
If the control engine name disappears from the Control Engine dialog, add the control engine name again to correct the problem. Use Add from the Select Control Engine dialog to re-add the control engine to the Configured Control Engines list.
Opto 22 is aware of this issue.