It is not a configuration problem. When the print writer was started it was started for a specific forms type (usually *STD). Now there is an entry in the output queue that is connected to that printer and it has a forms type of INVOICE. So it is asking you to change forms. (You may not want to print an invoice on blank paper).
To get a better understanding, use the F1 HELP on the message to get the lower level help. This will explain all the options G B I H R C