You are seeing the below error message on an invoice after attempting to publish it.
The cheque number you entered is out of sequence. Would you like to use the next available cheque number instead?
Sage 50 Canada users publishing Purchase invoices/Bills.
This error is caused by a cheque number already existing within Sage 50 for a particular invoice.
To fix this error, please allocate a different cheque number to the invoice, and republish it.