IcallBackEventHandler and Master-Content page

I have a custom control which  implements the IcallBackEvent handler which does asynchronous postback to server from client side.
When i put the custom user control on web form, it works fine. But when I put the custom user control in the content pages of master page, it does not work.  

These functions do not get invoked - RaiseCallbackEvent and GetCallbackResult

Getting the following error:

The target 'xxx' for the callback could not be found or did not implement ICallbackEventHandler.