I would say because 'cream': 0 should not be included in the recipe. If you omit it, you have a non zero solution... based on most code, cream:0 would cause an exception.

I made an error in my code. It is now solved.
I'll remove the thread in a day or so as it adds no value.

Thanks @hobovsky.

I passed the tests but have repeating errors in the attempt phase... 30 or so 1 should be 2s.. no idea where I am wrong.. it works for all the tests I have thrown at it. I am using the datetime library checking all the 13ths of each month of the input year to see if they are a friday.