This is a software and/or OS issue, not a hardware problem (the scanner plus ScanGear work fine together).

Updated to Win 8.1 about 10 days ago, no serious problems, all previously installed programs working normally (or for a value of normal relative to Windows!).

Up until yesterday, I was able to launch directly from photo programs (FastStone, Irfanview, XnView, Zoner Photo Studio) into the Canon CanoScan 9000f ScanGear software interface, then scanning, then go back to the original program.

Yesterday, I installed a small program for converting .dbf files to .csv (Exportizer). Now, when I try to scan, the Windows scanner interface window pops up (the same one that I used in Win XP!). This adds two extra steps to the scanning process: Windows preview then scan, which opens the Canon interface; this also eliminates the extra tweaks/adjustments available in ScanGear.

I've done the following: un-installed Exportizer (neglected to set a restore point!); re-installed the Canon software from disc; installed the current drivers from the Canon website (turned out to be the same version I already had); removed the scanner from the computer, then let the computer find it again. I searched the registry for the word twain, but my limited knowledge didn't see any results relative to my level of expertise. No malware found.

For some reason, "acquiring" an image from my scanner now launches the Windows scanner dialogue, instead of ScanGear. I'm close to deciding to run sfc /scannow, then Dism /Online /Cleanup-Image /RestoreHealth if needed. Is that a bad idea? (Fixed some problems prior to the Win 8.1 upgrade.)

Any ideas/suggestions?

--George

[FWIW, I've also posted this over at the MajorGeeks forum.]