Where you might be having problems...Crystal as far as variables is case sensitive. Also, if you formula is toggling a switch on and off, if the first record sets it on, and you are expecting your footer to do something, and the second record toggles it off...should the footer still do something or should it ignore.
Just something to think about. Try starting with a simple formula and place it in your details section...if Table.field="c" then true else false, and build from there.