Windows Phone 7, can only support up to 15 apps with push notifications at the same time, early users have been discovering. Opening more than one notification per app returns the same ‘InvalidOperationException(Channel quota exceeded)’ error message and applies not only to the live tiles on the WP7 home screen but also other apps with push enabled.
No current way exists to find how many apps are using push, and there is no global setting to be found in WP7, forcing users to open each app and enable or disable push from there. Microsoft is reportedly fully aware of this and designed WP7 to work in this fashion.
