iMessage not syncing between iPad and iPhone

My iPhone 4 an iPad 2 are both on iOS 5.0. After setp up iMessage feature, iMessage works fine on the devices. But today I find that the iMessage is not syncing between iPad and iPhone that are using the same Apple ID. When I receive the message on the iPhone, it doesn't show up on my iPad.Make sure the same Caller ID address set on both devices by tapping Settings > Messages > Recieve At >