To avoid the error, set up a condition within the formula to first check if the divisor is zero.

Example:
If {Field2} <> 0 then {Field1}/{Field2} else 0

It may also be helpful to check if there are any stray or extra division (/) characters in your formula:

Example:
{Field1}  + {Field2} +/ {Field3} should be {Field1}  + {Field2} + {Field3}