This update fixes an issue that could impact cellular performance and reliability for iPhone 4S." The iOS 6.1.1 update is a hefty 968MB. Meanwhile, some Apple iPhone 5 users have complained about what they perceive to be excessive battery drain on iOS 6 and some models of the phone are still having problems connecting to Microsoft Exchange servers since the launch of iOS 6. Apple has not said when it would release a fix for that problem. Until the problem is resolved, some corporate users will continue to block functrions related to corporate invitations.
source: AppleSupport via TheGuardian