We don't know why it happens, but occassionally our workstations get disconnected from the MOM server and we see errors like this. When this happens, we close MOM on the workstation, reopen MOM, reopen the order we were working on, and fix any errors we find.
Most likely that is what happened to you. We are also on 5.4.
I appreciate the response. but this is actually company wide. It's happening to all the computers in the building. I've rebooted every machine and the server and I'm still getting this message. I've fixed a lot of MOM crashes before, but this one is stumping me.