Random.Next() working only for restricted time/number of invokes?

I've been using a code that runs "forever" with a static random in one of classes. All works fine, numbers are random and there's no problem... for a restricted time (or number of invokes, not sure). After some time it starts to generate the same number all the time.

And here's the question: do you know of any time limitations over random class? Have you ever had such a problem?

I've changed the code and I'll now in like a week or two if that helped (each x minutes I create new object), but I'd like to know what's behind that and what should I be more careful about in future.