Hi, I had the same problem for over 6 months and stumbled upon an answer on experts-exchange. I did the standard uninstall, re-install, repeat for v2.3, 2.71, but nothing fixed the problem. The solution below works the first time, end of story.
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Answer by z3019494
Add the path to where Network Scangear is installed (generally %programfiles%\Canon\Network Scangear (for windows 32 bit) or %programfiles(x86)%\Canon\Network Scangear) to Windows 64 bit machines.
Do this by right clicking My Computer, Properties, Advanced System Settings, Environment Variables. In the System Variables, edit the "PATH" variable, append the abovementioned location to the path.
Good luck to all of you out there with this problem. I really like to know why this application stopped working all of sudden when no changes were made to scangear as far as I know.