Where do I find a twain driver for the scanner?

Fixed mine. There are no Windows 8 drivers available on Canon's website or Windows Update. Follow these steps to install a Canoscan 8400F scanner under Windows 8 x64 in desktop mode:

(1) Download and install the Windows 7 x64 drivers from the Canon website.

(2) Launch Device Manager, right-click and uninstall any (?) unknown device, then rescan for new hardware and the Windows 7 x64 drivers will automatically install.

(3) Download and install the Canoscan Toolbox software from the Canon website.

(4) Launch the Canoscan Toolbox software, select Settings, and click the Reset button to repair the non-working Copy/Scan/PDF/Email scanner buttons.

(5) Reboot.

Button functionality is restored after the reboot. Everything works as designed now. Good luck!

Easy fix for Windows 10 pro

To get the Twain driver download and install VueScan for Windows (I have v 9.5.25), it is only a demo. Install Canoscan - it won't run yet.

Run a scan with VueScan and your 8400f should run - don't worry about the watermark. Shut VueScan down. Run Canoscan and it should run as you want with twain driver attached. To check all is well shut your system down, reboot, and rerun Canoscan. If it works o.k. uninstall VueScan and you should be in business.

VueScan attaches the Twain driver for you.

Tried same things as above.

1. Canoscan N1240U scanner
2. driver not installed, and cannot find TWAIN device.
3. ASUS CM1745-5
4. nothing happens if I try to scan.

Dear Sir,

I tried to reply u via yr provided email address MicrosoftAnswers@microsoft.com but not successful. BTW, hereby is my answer...

1. HP OfficeJet 6500 AIO printer
2. & 4. No problem for printing & fax. While scanning, an error message 8, [(0,18,-2147467259)] is occurred and the scan process is failed.
3. Lenovo B570

 

I also used the printer & scanner diagnostic utility to check the device, it prompted that TWAIN driver error. However, when I used the MS Paint and scan a document, it worked successfully. Also, I reported this error to HP tech support but cannot get any answer. Do u have any idea to fix this problem? 

Tks for yr help.

Dear Sir,

I haven't received any reply. Do u have any answer on my query? Pls adv.

Dear Sir,

I tried to reply u via yr provided email address MicrosoftAnswers@microsoft.com but not successful. BTW, hereby is my answer...

1. HP OfficeJet 6500 AIO printer
2. & 4. No problem for printing & fax. While scanning, an error message 8, [(0,18,-2147467259)] is occurred and the scan process is failed.
3. Lenovo B570

I also used the printer & scanner diagnostic utility to check the device, it prompted that TWAIN driver error. However, when I used the MS Paint and scan a document, it worked successfully. Also, I reported this error to HP tech support but cannot get any answer. Do u have any idea to fix this problem? 

Tks for yr help.