It's not clear exactly what "can't enter" means.
First of all, the tag below your question says you are using TurboTax Online. In TurboTax Online you cannot make any entries directly on the worksheets. Everything has to be entered through the question-and-answer interview.
If you are actually using the CD/Download TurboTax software, what exactly happens when you try to enter the Zip code? The Property Information section of the Casualty and Theft Worksheet has an expandable list of properties. You cannot make any entries on the lines for the second property until you enter some information for the first property. Are you trying to enter a Zip code on line b for the second property before you have entered anything for the first property?
Entering information in forms mode can be tricky and lead to errors. You will probably find it easier if you enter your casualty or theft information in the Step-by-Step interview instead of in forms mode.