This or a similar error will be logged into event viewer after the OCR service restart
Engine pool with an Outproc loaded is used
The timeout before engine kill is set to 5000
if (_engProcess.WaitForExit(5000) == false)
OCR service is restarted right after processing is finished
The error happened because FineReader Engine was not able to remove engine instance after processing, however, the time interval specified before the kill command is still in progress, thus restarting the OCR service may log an error related to engine instance inactivity.
Increase or decrease time before the kill command, in order to remove the engine instance, in any case, if the OCR service is restarted after time has passed the error will not be logged.