I was trying to add keyboard shortcuts to Photoshop CS5, after watching the ctrlpaint tutorial, using function keys. I was able to map F3, F4 and F5 to Zoom Out, Zoom In and Fit to Screen just fine.
I think I closed Photoshop and opened again, and tried to assign other function keys but it now says, on trying to assign:
F3 is an invalid shortcut. The F-key cannot be used.
for any of the function keys, even if I try to assign the F3-5 again. I read on the Adobe website that F1 can't be used, which is fine, but I'm uncertain why the others won't assign anymore.
I'm running Windows 7 Ultimate 64-bit and Photoshop CS5 Extended, with a UK keyboard layout (and Microsoft Keyboard).