Do you have a standalone scanner?
I've found sane/xsane every disappointing. So much so I finally installed ms-XP in VirtualBox and the HP drivers into Xp and run that combination when I need to scan, which is every day.
Apparently, it depends on the chip in your scanner and how well it is supported by sane. As to "device busy"..... sorry, nothing comes to mind (at the moment, but I'm losing my mind in my age
)
BTW, how did you install the printer?
From trial and error I've found using a browser, going to "localhost:631" and picking the hpijs driver works best.