This is caused by making some invalid change to items on the invoice in SuccessWare21.
Regardless of the cause, this can be resolved by performing the following actions:
- Locate the part or task corresponding to the ItemNumber that is given in the error message
- Remove the offending part or task
- Add the part or task back to the invoice
You can follow the steps found HERE for help removing and adding parts to the invoice. If this comes up frequently, the best course of action would be to contact SuccessWare21 support at 1-888-251-2779.