have you checked the compatibility in the user manual? different iOS devices use different USB technology.
If it's compatible, you could try turning off/on bluetooth or the iPhone itself.
If that fails, you could also try restoring the device as new. If that doesn't solve the issue, the device may need service.
Follow the steps in: http://support.apple.com/kb/HT4137
NB: set up as a NEW device because a software issue will be in the backup. If the issue persists after restoring as new, you should offer the device for service.
I also recommend you try connecting the iPad to other bluetooth devices to make sure the issue is at the iPad.