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 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.

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

Showing 27 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!!

  • TC

    Thanks, worked for me

  • Aaron Wong

    !!!! Thanks! Worked immediately for me! Thank you so much!

  • Mark P

    Genius – quick and easy solution, and my ~15 year old Canoscan 8400f continues to prove its quality and utility under Windows 10.

    Editing the environmental variable was slightly different on my system – it brings up a window and lists each part of the PATH variable separately and allows you to edit, delete or add – but it was simple enough (for me) to work out.

    This definitely wasn’t an obvious solution, and even though I’m technically-minded, I don’t think I’d have ever (previously) thought of looking in this part of the system for the solution!

    Thanks again

  • b00d

    You are the man Garth! I was about to drop $60 on VueScan which is worth more than a new WIA compatible scanner, and more than this CanoScan LiDE 500F cost me! CanoScan and ScanGear both work great now, the folder I had to add to the Path variable was “C:\Windows\twain_32\CNQL500”

  • Hans de Bruijn

    In needed the solution desperately. Many thanks! Worked immediately. I salute you!
    I had to change the path c:\windows\twain_32\CNQL25 slightly. Only the last part I had to adjust.

  • Andrei

    Thank you very much ! My CanonScan did not work since I changed my PC from XP to W7. By chance I saw your post, it works now, great !!!

  • Sherwin

    Thank you this fixed my scanner for me. I used both the C:\Windows\twain_32\CNQL25\ and C:\CanoScan\CNQL25\

  • DonaldTrap

    After upgrade from xp to w7 had to install canon lide 60 drivers to make lide 35 work, after upgrade to w10 scanner was recognized but no software was able to open twain, after half a day of struggling i found this post, it took me 30 seconds to fix it and now it’s working flawless. Tnx a lot u saved me hours of swearing

  • Robert T

    Worked great! Thanks so much, very clear directions, easy to do. Thank goodness, I’ve been struggling with this off and on (according to my discouragement level) for months now, ever since upgrading to Windows 10. Fantastic!

  • roger

    Thank you
    You saved my scanner.
    It bothered me to have such a big printer at home so the scanner wouldn’t work. (Canon Ir2028i)

  • D

    Obviouslly , toolbox software should add this environment variable at install
    great workarround , thank you.

  • Skrblik

    THX dude, works for me.

  • James W Troy

    This was a very helpful article. Thank you very much !

  • simonsen

    This article brought my old CanoScan 9950F back to life. Thank You!

  • LM

    You’re great! I solved the problem with your article. Thank…

  • Al


    I’m not very savvy with this but could get to the variables path in win 10. I have an old LIDE60 scanner that was giving me the same error message. Do I just copy and paste the location of my scanner into the path area.? Won’t this affect other programs? Thanks

    • Garth Jones (Admin)

      Yes that is right just copy and paste the path and no it will not affect other programs.

Leave a Comment

Share via
Copy link