OES and OCAS - How on earth does this work?

Results:
OES: 81
OCAS: 36

I've just had a huge shock to find that I have failed my module overall. My "OCAS" result for my TMA01 and TMA02 was a pathetic 36 average. I was undergoing a lot of stress at the time (estranged from my father, hit by a car, lost my job) and the OU has been made aware of this. I was disappointed in my mark but made an extra effort in my iCMA and EMA to bring up my average, thinking that this would pull up my score and mean that I would pass the module. 

I have just discovered this is not so as, although I recieved 81 for the "OES" result, because I only got 36 in the "OCAS" I have failed the module. 

I thought all of the assignments added together and your module result was that average? Why is it split into two average as I would have passed with an average of 58.5 if this was not the case?

I am very confused!