Can't Scan With Canon Pixma MX700

Back in the fall when I switched over to Windows 7 Home Premium x64 from Vista Home Premium SP2 x64, I installed the software for my Canon Pixma MX700 multifunctional printer. I used the original Vista driver installer disc, and despite an warning message about a "known compatibility issue" the printer and scanning functions worked fine. I use the Pixma on the LAN via a wired ethernet connection. Worked fine for occasional scanning in November, December, and January.Then for months I had no need to scan anything, just printing over the network with no problems.Last weekend I needed to scan something. I usually just push the scan button on the printer, verify the computer it's going to scan to (it lists them), and away it goes. This time my computer threw an error about the scanner driver saying the scanner wasn't on the network. Huh? If the scanner's not on the network how did the computer know it was trying to send a scan... So I bailed on that and instead used the MP Navigator EX software on the computer. It failed too, giving the "scanner not connected" error, either using Navigator's direct interface or telling it to open the scanner driver which brings up a slightly different interface (when it worked).First I went to the Canon site and d/l'ed all the latest drivers for 7 x64 and installed them. Still get the same errors. Tried setting it up to scan via USB temporary connection. If I install it that way it works, but it's not a long term solution. And it stops working after a reboot. The odd thing is the scanner works over the LAN after I set it up for USB (when using NAvigator, because the scan to lan button on the printer doesn't work of course), again until reboot.