Can't access network scanner

[MR ZenWiz]

I use xsane (and will ask there, too) and for some reason, my Xubuntu
laptop cannot detect or connect to the network scanner at one of my
locations.

I can print to the printer just fine (it's an HP Envy 4500), and the
sane backends page shows this as being part of the hp5590 back end,
which I have installed.

What am I missing?

Thanks.
MR