Inter-Project Billing -- Error in Tieback Process

I have implemented Inter-Project Billing. All processes are working up to the Tieback Invoices from Receivables process. The invoice transfer to the Receiver OU's AP module is rejecting with the error message "No project/task for Inter-Project inv".

- Provider controls are set in the Provider OU.

- Receiver controls are set in the Receiver OU.

- The Provider project is set up with the "Bill Another Project" box checked, and the Receiver project and task selected on the Customers and Contacts form.

- The task on the Receiver project is set to allow charges, is set to be billable, and both the top and sub tasks have the "Receive Inter-Project Invoices" box checked.