Two paycheques have been assigned the same cheque number
MYOB Accounting Plus allows you to assign the same cheque number to multiple paycheques. Depending upon how your preferences have been set, a message may appear to alert you when you print or record the paycheque, and you'll be given the option to cancel printing and change the number. (If this message wasn't displayed and you'd like it to be in the future, open the Preferences window, choose the Banking view and mark the "Warn for Duplicate Cheque Numbers" option.)
Once a paycheque is recorded, the cheque number can't be changed. If you didn't intend to assign a duplicate cheque number to the second paycheque and you wish to change it, you'll have to either delete or reverse the paycheque, then reenter it with the correct information. Whether you will need to delete the paycheque or reverse it depends upon how your preferences have been set. (Choosing changeable or unchangeable transactions)