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Canon Scanner – Unable to Open TWAIN Source

By Garth Jones

Recently I replaced my laptop and one of the important things that I needed to get working on it was my Canon LiDE25 scanner. Each time I replace my laptop (which happens frequently enough) I encounter the same problem, so I thought that I would share with all of you how to solve this issue because it can be a bit annoying.

Below is the error message that I always get:

Canon Scanner - Error Message

Unable to open TWAIN source
Please check connection
Then re-start Toolbox

The problem is that the TWAIN drivers are not within the system variables path.

What I do first is open the Control Panel.

Canon Scanner - Control Panel

Next I click System and Security.

Canon Scanner - System and Security

Then I click System.

Canon Scanner - Advanced System Setting

Next, I click Advanced system settings.

Canon Scanner - Environment Variables

Then, I click Environment Variables…

Canon Scanner - Path

Then I scroll down on the system variables and find the Path, highlight it and then click Edit.

Canon Scanner - Path Name

Next I add the path name for my TWAIN driver to the Path system variable. In this case, it is c:\windows\twain_32\CNQL25. Lastly, I click OK three times to return to the Control Panel, and then I exit the Control Panel.

Canon Scanner - Scanning

Finally, I restart the CanonScan Toolbox. Now my scanner works without any issues and the same should be true with your scanner.