unable to open twain source - canoscan Lide 500F

In Windows 8 :: Go to Control Panel > In search type 'Environment' and there you will see an option that says 'Edit the system environment variables' so click on it > in the Advanced tab click on 'Environment Variables' > On System Variables click on 'New' > type Variable name: Path, and Variable value: %SystemRoot%\system32;%SystemRoot%; C:\Windows\twain_32\CNQL25 (the 25 number is the number of your scanner, my scanner is 25) > click on OK and OK. must work.

I had this problem on windows 8.1 and with a canon 4200f.  Tried the path environment variable with latest canon software 5.0 but no luck.

Went here:

http://www.usa.canon.com/cusa/support/consumer/scanners/canoscan\_series/canoscan\_4200f#DriversAndSoftware

downloaded the drivers for windows 7 and canonscan 4.2 and it is fine.

I guess that the scanner is too old to work with the new software.

There is no software listed for 8.1

Best of luck

In Windows 8 :: Go to Control Panel > In search type 'Environment' and there you will see an option that says 'Edit the system environment variables' so click on it > in the Advanced tab click on 'Environment Variables' > On System Variables click on 'New' > type Variable name: Path, and Variable value: %SystemRoot%\system32;%SystemRoot%; C:\Windows\twain_32\CNQL25 (the 25 number is the number of your scanner, my scanner is 25) > click on OK and OK. must work.

Having checked the path variable I find that the "fix" you suggested is already in my path.  C:\Windows\twain_32\CNQL9950F but I still get the same problem.  I have another computer running W7 also and the variable is not in the path but it will still talk to the scanner.  Any other suggestions.

This did work previously but stopped working.

How do I find the scanner number?