I had an issue with the hash (#) key on my Mac.
I needed it cos of a product code i had to enter. Couldn't find it anywhere on the keyboard.
Turns out the 'omitted' (ie. - fucked up) it from the UK keyboard. Took me three days to find out. Very nearly was getting chucked through the window.
It was alt plus 3. Didn't say that anywhere on keyboard, manual or help though.