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 askgarth.com 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:
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.
Next I click System and Security.
Then I click System.
Next, I click Advanced system settings.
Then, I click Environment Variables…
Then I scroll down on the system variables and find the Path, highlight it and then click Edit.
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.
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.
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….
Did not work for me. Any suggestions?
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.
You shouldn’t have to do that but if it works that is great!
You are a genius and a scholar! That worked! Thank you!
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
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!
I love you, the path setting fixed it for me.
you are greaaaaaaaaaat. thx a lot
You are the best! Thanks for this! No telling how long I would’ve searched w/o you!!
Thanks, worked for me
!!!! Thanks! Worked immediately for me! Thank you so much!
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!
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”
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.
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 !!!
Thank you this fixed my scanner for me. I used both the C:\Windows\twain_32\CNQL25\ and C:\CanoScan\CNQL25\
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
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!
You saved my scanner.
It bothered me to have such a big printer at home so the scanner wouldn’t work. (Canon Ir2028i)
Obviouslly , toolbox software should add this environment variable at install
great workarround , thank you.
THX dude, works for me.
This was a very helpful article. Thank you very much !
This article brought my old CanoScan 9950F back to life. Thank You!
What path name did you use for your 9950F?
You’re great! I solved the problem with your article. Thank…
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
Yes that is right just copy and paste the path and no it will not affect other programs.
This is still work !!!
My Canon 4400F refuse to scan since one week. I have use it since 2016 on windows 10 with no problems since last week until I have this twain error.
Uninstall, install driver Canoscan toolbox 5.0 .
I have try your solution and Bang Scan Again !!!
I needed to use my trusty Canon scanner in a hurry after a year of not using it, to get greeted by that message. I googled it to find this page and in 5 mins it was fixed and the scanner happily chugging away as only that bit of kit can.
Thanks very much for your altruism may your business continue to grow!
Since a week or so my MP800 (multifunctional) is unable to scan (printing is no problem). I tried your solution with no result. Confusing thing is that when i go to the printers and devices section, select the printer and try to scan using ‘scan control’ it does make a scan. So the device and the connections are ok. But MPNavigator-2 is not starting the scanning software nor does the Windows 10 Scan app. The latter does find the device, but fails to start the scanning software. I’ve been uninstalling and reinstalling drivers, setting compatibility to windows 7, performed a “scannow” and what not, but it stays stuck. I’m out of ideas. Any suggestions are welcome
Cool. Thanks man, this fixed it for me.
This solution was just what I needed! I was one second away from giving away the scanner but now it works!
Glad that I could help.
Thanks for your efforts seeking out this fix, now my scanner functions again like it always used to. DA
Glad it helped.
Thanks! Works perfectly!