A problem similar to ours was reported here, but handled offline, so I can't follow it to a solution.
http://www.objectiflune.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=48;t=000518
Following as best I know how an exact procedure results in success (production of a .PDF output file) or failure (only the .DAT file is produced in the output folder). I can produce success and failure two minutes apart.
The Watch console error codes that accompany failure are:
I0012: Error merging: Error opening source file: Error code 5: Access is denied.
and --
I0006: PlanetPress Image output failed on host 127.0.0.1
PlanetPress Image: W1603: Plugin failed - 15:28:32
The discussions I've read so far have approached the problem as if it is consistently occurring. For us, it's intermittent.
The workaround has been to "run the job again" but that's getting old.
Any assistance will be greatly appreciated.