Reservation Entry does not exist Error

I have a situation where Reservation Entries are created manually from Production Orders, and sometimes the order is invoiced before it is produced (and at this point the reservation is cancelled to allow this to happen). This creates an orphan Reservation Entry, and when a Sales Credit Memo is created against this invoice, it generates the following error:

The Reservation Entry does not exist.

Identification fields and values:

Entry No.=‘00000000’,Positive=‘Yes’

We are using NAV 5.0 sp1.