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 within SWRemote:
- 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.