Carry both with you. My husband recently got a new passport, but had to travel for business before he was able to get a new visa. So, he was told to carry both. You will need to show your most recent passport, since that is the only one valid. (so try just showing that, and see if it works). If they question you, then you can pull out the old passport, to show that the visa was issued with your old passport. Shouldn't be a problem since you have a passport and visa... Might take a few extra minutes, but don't worry. (fortunatly, this is not Saudi, so don't worry about getting detained, as someone else suggested)