Question about Canon CanoScan D646U Flatbed Scanner

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Canon Flatbed scanner model D646U ex for Windows XP

After days of struggling trying to install de XP version for this scanner I finally suceed and got it installed, but when it opens and try to scan something an error message is displayed saying:"Unable to open TWAIN source, check connesction and the restart toolbox".
I checked all connections and everything seems to be ok, what could be the problem?
Please help
Jacinto Gordón Jr,
Republic of Panamá

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Could be a problem with the cables themselves. Try a new set or different set of cables and see if this resolves the issue. Also make sure that you installed the correct version of the driver for your OS.
Should you still have difficulties, try a clean boot as explained below:

(Just replace "camera" in the procedure for scanner.)

Posted on May 15, 2008

  • Swilin Sampson
    Swilin Sampson May 31, 2008


    This thread has gone 14 days or more without a response.
    Please close the thread with a “FixYa” or “Helpful” rating.

    Or post back with latest developments, what steps you took,
    etc. and I will assist you further as best I can.

    Thank you.




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Hi jurjenweerma
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Hi ,i need the software for canoscan d646u ex for vista thanks

I am sorry to tell you that the driver does not exist for vista.

But you can try the one for windows XP from here:

Hope this was helpfull.

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