question

The issue is being caused by using multiple Wait for Event activity that reference the same Processor as their Object. For instance, sometimes you might have two boxes enter the same Processor and the respective tokens will both be sitting on different Wait for Event activities waiting for the Processor's SendToPort to fire. However, when the first box fires the SendToPort, both tokens will advance in the Process Flow. This will cause some boxes to be moved to the Sink before they have finished being processed on their current Processor. This will throw an error because the Processor still thinks it needs to finish processing a box that is now destroyed.

You can avoid these errors by using the Label Matching/Assignment field of the Wait for Event activities. You just need to set the Label Name to be item and the Operation to be match for all your Wait for Event activities.

Another thing I noticed is on the right side Acq_Paint section of activities in your Process Flow. The Move Object activity is moving boxes to the Proc_Inspection Processor. From the rest of the logic, I believe this should be moving the box to the Proc_Painting Processor instead.