The Ref! error

Hi,

 I'm working on my uni assignment within excel and am using the CAPM formula to work out the expected return of the market data I have inputted. The calculation is as follows =M124+M123(M122-M124).

This brings up the REF! error. None of the info within the cells has been copied/cut there and I cant see another reason why its coming up. M123 +M122 are data calculations and M124 is just a number that I entered.

I have also screenshot the excel page if this helps.

Regards,

Kofi