some ridiculous crap today…i tried to scan a document on a canon canoscan scanner that i’ve had attached to this PC for 3 years. in those 3 years i’ve never messed with the canon software besides initial install. in those 3 years everything worked fine until today. i received an error message along the lines of “unable to open twain source…” and was unable to scan anything. windows device manager still showed the scanner fine. the only significant changes i’ve made to the machine are windows updates.

since i work in IT i expect stuff to break, but i always get really agitated when some super basic function stops working. the things you take for granted like: opening up your word processor, email client, web browser, file manager…or printing/scanning a document.

luckily, the first google search result led to a well organized and concise blog entry. my thanks to the author jeff.

the solution (heavily summarized) is to edit the system environment variable PATH and add the path “C:\Windows\twain_32\C*”.
for me, the C* subfolder was “CNQL35”, but this will evidently vary based on what model scanner you have.

source:
http://weblogs.asp.net/jeffwids/archive/2009/11/02/canon-scanner-unable-to-open-twain-source.aspx