CUPS permissions (after install rescue)

I had an install go awry but with this community's help managed to get it back on the rails, as described in this thread:

https://trisquel.info/en/forum/issue-grub-and-existing-home-partition-installing-trisquel-mini

Now I'm doing some cleanup and one issue I have is that I can't add a printer. Using "Printers" GUI utility (I'm using XFCE but that's probably irrelevant), when I click "Add" I get the usual CUPS window but a dialog box asking for my user name and password also appears. I enter my user name and password but it's not accepted.

While I'm at it, are there other permissions or cleanup activities I should check into?

Thanks in advance!