If this happens it might be that the bill needs reversing and the WIP attaching to the new bill:
From the main menu go into General Postings.
Select SIB and tick the reversal box.
click NEW.
You can then pick up the bill to reverse on that matter.
Select the Floppy Disk icon to save.
Select POST.
N.B
If there is an allocation against the bill then this will also need to be reversed before doing the SIB reversal.
If this doesn't work, please raise a new case online and reference the title of this article.