APP-INV-05505 message

Hi I am encountering this error message ( you cannot update this field when there is on-hand quantity or transactiosn exist) when I am trying to change the serial gneeration at the organization item form.  I checked the onhand quantity (it's zero) and there is no pending transactions, nor records in the open interface table.  There is also no reservation nor move transactions.  Can someone advise what else I need to check or what I may have missed?  Thanks!