There are several possibilities for this error in my opinion. Is PO20 one of your more heavily used programs? have you ever looked in tmmon while this was happening. That's a nice tool to have real-time look at what's going on with your lacobrts sessions. Often times when there is a message like this one of the other logs will have more information. Did any other logs get hit in $LAWDIR/system ? A lot of times there is also a lapm log in $LAWDIR/system/joblog that has info.
If tmmon is not a tool you commonly use ... it can be accessed by typing tmmon at the command line in LID. you'll want the refresh rate set at 1.