Yesterday I had a project working without problem with Xcode 5. Today, after the update to Xcode 5.1 i have 6 errors and the project is not compiling.
Undefi
i think the paypal library you are using, does not support arm64.
check this PayPal-iOS-SDK issue-47 for the updated paypal library.
Edit :- update link for paypal library (with arm64 support)