Ok, Joomfish now requires a column alias if the same column is used in the criteria for a query. I have amended the code to take account of this, and applied the change to your site, which seems to be working ok now. For the benefit of anyone else who wants to take advantage of this, here is a replacement /administrator/components/com_nbill/admin.proc/invoices.php file (which will be included in the next release of nBill).
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