What is going on here?

Hello,

So i am trying to do some basic math which i have done before yet i get an error.. Anyone have any idea why?

the function I am trying to run to populate a Double Field: math.atan2( !DeltaY! , !DeltaX! ) *180/3.14159

the error is: <type 'exceptions.TypeError'>:a float is required

I have never seen this before while running this particular formula. What is going on?

Thanks