I'm a beginner, and have very limited knowledge of such things-
but, my scratch disc size wasn't large enough to handle even small images at some point.
I defragmented my hard drive purged the caches, knocked out some unused applications and tossed tons of awful exposures.
Now my crashes are minimized(although CS4PS photomerge at more than a gig will do it)
also, my thought is there is a glitch.
Hmmm what I mean, is my z3100 sometimes just has a little tantrum and refuses to get up off the floor without serving a time out in the corner.
Really, shut off the computer, unplug the USB to all devices, power down the printer according to the manual, shut off the printer power toggle in the back of the printer near the power cord, let it set for a moment, turn back on the printer and computer, and then plug in the USB to the printer only.
My seagate external drive really was fouling up the actions I was taking, coming on unexpectedly, adding a layer of hocus pocus to an already demanding pursuit.
Now it all seems to be meshing, but still once in a while the computer won't detect the device or some other thing like you're talking about.
Maybe I'm lucky and the power trick has worked every time so far.