Old fashioned fudge can be temperamental.
I agree with Silversage about beating the fudge to improve the consistency/texture of the finished product.
These days I would go with a modern recipe that uses marshmallow cream or sweetened condensed milk.
This recipe for vanilla fudge will give you a creamy texture similar to a truffle, it is expensive compared to the old fashioned recipes but it is pretty much foolproof.
Creamy White Fudge