I have set up the Total budget field to divide by the project rebate amount and then output to the bottom left one then the same but for the other budget field output to the CN budget field. I keep getting this error though when anything is typed into the form. I am making this form for others to fill this out so I need the fields to be blank for them to type.
You're getting this error because nothing is typed in the form. This means the divisor is being interpreted as zero, which is not allowed, so the result is NaN (Not a Number) and can't be assigned to a field with the Number format.
To overcome this you have to use a script that checks the second field's value, and if it's not empty (or zero) proceeds with the calculation.