How are you comparing your returned results against your calculated ones? First of all, your coefficients are being generated as doubles but being displayed as integers, so if you are basing your calculations off of the coefficients listed in coeficienti then they are not going to line up. Secondly, if you followed as Ravens had suggested and looked at the advanced help for the polynomial roots VI you would see that there are a number of different calculation methods, and the default Simple classification is not going to be as exact with the calculation.
Consider changing these things and you should be getting the correct results.
