Hey, (ACA 2012)

I've been working on the office 'shortcut keys' lately and I've run into complications. Don't know if it's because of something I've done or if these are 'normal' problems.
I can't assign commands to these combinations:
Ctrl+F1 - Ctrl+F4 - Ctrl+F6 - Ctrl+F10

I don't think these are Windows combinations and I don't have any commands already assigned to these combinations.

Also, I'd like to assign a command (add wall) to SHIFT+W. However, this combination is already assigned to 'navswheel', and I can't figure out how to change it.

Any thoughts would be appreciated.
Thanks

Pierre P.