Canon Scanner – Unable to Open TWAIN Source

by | Dec 18, 2014 | How-To | 38 comments

Last updated on August 2nd, 2022 at 10:27 am

Recently I replaced my laptop and one of the important things that I needed to get working on it was my Canon LiDE25 scanner that I used for tasks. Each time I replace my laptop (which happens frequently enough) I encounter the same problem with this Canon scanner, so I thought that I would share with all of you how to solve this issue because it can be a bit annoying. BTW you can download the Canon Scanner software on their site. Just as an aside, I need to do this on my Windows 10 and Windows 11 computers too!

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 computer system variables path.

How to Solve the Canon Scanner – Unable to Open TWAIN Source Error

This problem took a while for me to find and solve . But one you know what the problem is the solution is easily fixed.

What I do first is open the Control Panel.

Control Panel

Next I click System and Security.

System and Security

Then I click System.

Advanced System Setting

Next, I click Advanced system settings.

System Properties

Then, I click Environment Variables…

Environment Variables

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 Canon scanner works without any issues and the same should be true with your scanner.

I hope this solved your problems with your Canon Scanner. if you have questions you can always tweet me @garthmj. I will do my best to get back to you once I see it.