Same setup here, same issue. I've got my C5180 connected to a D-Link W-(something or other) N-band router via ethernet. My 2.2 Ghz (late 2007) Macbook pro, running 10.5.6 and with the latest HP drivers, has issues. It can print flawlessly - as long as I'm connected to the network (ethernet or wifi), it works great. Yet, scanning doesn't work - it gives the same error.
Printing works fine either with the OS X included HP drivers or the HP drivers, but scanning doesn't work worth a darn. Bummer, that, it's a nice machine. I've had to resort to scanning to the memory card, which due to the low resolution it defaults to (and poor color settings), is limited mostly to scanning documents to images. For some odd reason, scanning actually "works" on my old iMac (DVSE - 500 mhz G3 - 10.4.11, 512 RAM) - at least it can initialize the scanner. Of course, the HP scan pro immediately crashes when I attempt to scan, and is slow as molasses running uphill in january, but at least it connects... It WILL usually work under Boot camp with XP SP3, but that's a pain.
Sadly, Photoshop, Image capture, and others have to go through the HP app to scan, although it can do it automatically - if only the app worked.
Is there a third-party driver, or software package, for the scanner? My next printer/scanner will NOT be an HP, but the printer at least works very well - there's no reason to upgrade apart from the scanner issue.
-Dan