✅ System.FormatException

Me and another are writing a RPN calculator.
I get this error message when trying to calculate

3 4.8 5.7 + * 2.5 *

3 4.8 5.7 + * 2.5 *

but when he runs it he does not get an exception on it. We have the exact same files and code. Why?

✅ System.FormatException - C#