Keyboard Shortcuts - can't create or edit

If I try to change a keyboard shortcut, I just get a msg that “the selected shortcut is not allowed…”

How can I add a new shortcut or modify existing ones because the program won’t let me type anything in the shortcut box.

Hello Kerith,
you do no type the shortcut, you just need to hold the combination of keys you want to use as Shortcut.
The warning just specifies that a valid shortcut needs to include CTRL, SHIFT, ALT or they can be the Function keys.
Start your shortcut with one of these keys and it will work.

Adding new shortcuts is not possible, you can just edit existing ones.