Some propositions don't deserve nonzero credence.

I think that, 

    1) We should assign nonzero credences even to things we deem impossible.

My intuition here is that I may be wrong about what is and isn't possible. I think things popping into existence uncaused is impossible, but maybe I'm wrong. I think contradictions are impossible, but maybe dialetheism is true. Etc. But consider,

    2) The probability that event E (say, a fair coin landing heads) occurs is infinity.

I think (2) is impossible. It is impossible for a probability to be greater than one. However, according to (1), I should assign it a nonzero credence because I might be wrong. But I also believe that,

    3) If one has a credence p₁ in the proposition "The probability that event E occurs is p₂," then one's credence in the proposition "Event E occurs" should be equal to or greater than (p₁)(p₂).

Makes sense. If my dice is fair, then getting a six has a probability of 1/6. But if I am only 50% sure that my dice is fair, then I would be less confident that I will get a six. But I should have a credence of at least (1/2)(1/6) = (1/12) that I will get a six. But (1), (2), and (3) entail that,

    4) My credence in the proposition "Event E occurs" (say, a fair coin landing heads) should be equal to or greater than infinity.

So I should be infinitely certain that event E occurs. That's wrong. So, it looks like (1) is false.