iTunes 10.3 thinks it's a version below? No ping, locked out from iphone sync
You're in troubles. :(

How you updated your iphone to IOS5-beta without iTunes 10.5? Asking because iTunes 10.5 is only for developers now.

from the: http://www.appleinsider.com/articles/11/06/06/apple_says_devices_updated_to_ios_5_beta_cant_be_restored_to_earlier_versions.html

In releasing several pieces of pre-release software -- iTunes 10.5, Apple TV 2 beta, Xcode 4.2 Preview and Lion Preview 4 -- to its developer community, Apple on Monday warned testers of its new iOS 5.0 software that any devices updated to the beta cannot be reverted or downgraded to previous versions.

You need iTunes 10.5 - developer release yet - whats mean register yourself as developer for 99USD/year.