I have a spreadsheet with cells B4 to AC4 down to AC78. Each row has
28 fields that the user will either indicate a "1" or a "2" only once
on each row. ie. Row 4 could have cell E4 with a "1" row 5 G5 with
a "2" and so on.

I would like to be able to protect each row so that only once cell is
completed. ie. only "1" is filled in once, not twice.

I would like a message box to pop-up to state "Only one selection
allowed".

I started to work on the script but have not been sucessful.

thanks.

Mel