If this is already set, then for some reason the other machine isn't being seen as having rights on the network. It could be lack of user account password or other things.
Just browse for the printer like
\\PCNAME(name of PC sharing printer)\
then you will see the printer.
Right click and connect ad it will prompt you for credentials. You can save them there, then it shouldn't prompt you any more. But only do this as a last resort.
You may, then, have 2 of the same printers installed, delete one of them that didn't just get created.