I have tried running the Canon MP780 driver installer as Admin, without UAC, and in compatibility mode, But my Canon MP780 can not install correctly on Windows 7 x64.
Solved my Canon MP780 Printer problem.......You try another USB port! Plugged the printer and the driver files downloaded from the internet and all was well.
I found that windows 7 had already installed a mp780fax driver
1. Choose " add a local printer" then in "use an existing port" drop down menu, choose one of your "virtual USB ports".
2. Click windows update and wait.
I guarantee their is a canon MP780 printer driver