It happens mostly in Purchase Order and especially when they are trying to print.

At first, we had no idea what caused it.  Since it is random, it is really hard to pin this down.  The consultant later on went on site and several days later advised that the problem was fixed.  Based on the consultant feedback, it was caused by a network cable.  The user ran the patch cords under a carpet, and they were running over them with the wheels of their chairs. 

The cables were in bad shape.  After replacing the cables, they have not had the issue happen in a few days, so they know that the problem is fixed.