Canon Scanner – Unable to Open TWAIN Source

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.

Showing 10 comments
  • Mika Turpeinen

    Still working (FIX) with WIN 10. Obviously some latest Win 10 updates have made changes as I had not this path (manually added) ever before….

  • RM Duenas

    Did not work for me. Any suggestions?

    • Garth Jones (Admin)

      No Sorry.

      • spytsi

        I’d guess that you copied the path of your TWAIN from your Windows Explorer’s address line and pasted it to the path system variable, as suggested above, and no result, right? That’s what happened to me at first, too. But after looking carefully at the variable values already within the edited path, I noticed that all of them were ending with a backslash “\”. So, here’s my suggestion: when adding the path of your TWAIN, don’t forget to put a backslash at the end of it. In the example above, you should type C:\windows\twain_32\CNQL25\ instead of C:\windows\twain_32\CNQL25. This worked for me and I believe it will also do for you.

        • Garth Jones (Admin)

          You shouldn’t have to do that but if it works that is great!

    • Bernhard

      Look in the windows twain_32 folder, in my case it was C:\Windows\twain_32\CNQ4803 so, you can try adding all folders in twains_32 to the path. I imagine the CN***** folder has different names depending on what scanner or what install, so in my case i looked up, and put this folder in that I found in my system, no problem anymore.
      I don’t know, but I guess you could also lookup in the Twain_64 folder if there is something there that needs to be in the path

  • Scott

    That’s what it took! Thank you for posting this!! It really burns my behind when installer programmers think their program is the only program someone runs on their computer and completely wipes an environment variable instead of APPENDING to it!

  • Georg

    I love you, the path setting fixed it for me.

  • Iman

    hi there
    you are greaaaaaaaaaat. thx a lot

  • Ron

    You are the best! Thanks for this! No telling how long I would’ve searched w/o you!!

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