I got tired of this wia driver
problem with Windows 7, specially for x64. Just to share, this is how I solved my problem.
I have a Canoscan LiDE25, and of course, encountered the same problem with you even though we have downloaded the so called x64-bit drivers
from the manufacturer of our product. Yes the driver is there, however, the functionality of the scanner is gone as well.
1. Install again (or if you have another computer) on a computer with Windows XP the drivers and the software for the scanner, xp 32-bit version of course.
2. Go to folder windows and copy the twain_32 folder (on a USB, or any other portable devices from which you can transfer the files to the computer witn Windows 7 64-bit. For my part, for LiDE25 twain_32 folder contains two folders (CNQL25 and CNQSG plus a file named wiatwain.ds
3. Install the 64-bit driver (this is for the registry purposes only) on your windows 7 64-bit.
4. Now copy twain_32 folder (from winXP) into windows (of Windows 7, of course) and overwrite the whole of twain_32 folder.
5. For my scanner, i made a shortcut of the file SGST.exe (this is scangear, from the folder CNQSG) on to my desktop if I just have to use the scanner by itself.
6. Presto! It works! And all my other software now that needs to make a scan (CorelDRAW X5, AbbyFineReader, MSOffice, Adobe) can make a scan through their own context menu and can trigger and run scangear as if you are working with it from windows xp. No errors or whatsoever.
Note: tried and tested this procedure several times, thinking it might be a fluke. but it always work everytime. I hope this procedure will also work with other hardwares that always get the error "you need a WIA driver to use this..."
Now I can finally stay with Windows 7 64-bit (this is the only problem holding me from migrating to windows 7 64-bit)