Fix for Canon scanner error "Unable to open TWAIN source"

I discovered this on a Canon LIDE 25 scanner but it seems to apply to many Canon LIDE scanners. Sometimes the CanoScan Toolbar will fail to scan documents and give you an error along the lines of "Unable to open TWAIN source". You need to find the directory where the Canon TWAIN drivers were installed and add it to the path environment variable. Typically it is located in c:\windows\twain_32\cnqlXX. XX will vary depending on your particular model; for an LIDE25 it would be CNQL25. No restart is required.