You will need to log in to the system and identify the line that is causing the issue. You can do this by running the following script.
SELECT * FROM POADVICE WHERE Purchase_Order_No = '<PONUMBER>' AND Advice_Note_No = '<ANNUMBER>'
This will hopefully return the one affected line in question, if not use something else to return one record, usually you will find adding this line will work
AND Total_Value = '0'
Once you have returned the line that is causing the issue, check the line to make sure that the Invoice_Matched and the Invoice_Number fields are indeed blank.
Once you have confirmed they are, copy and paste the WHERE statement from above (or the one you used to return the single record if different) and DELETE the line as follows
DELETE FROM POADVICE WHERE Purchase_Order_No = '<PONUMBER>' AND Advice_Note_No = '<ANNUMBER>' AND Total_Value = '0'
Now when the user goes back into the affected areas, they will see the record has gone
