Webservice and callbackfunction??

Hello.
i am new to asp.net and webservices.
i am using a webservice which returns e.g(sum of two values) when i call it. i have used it in my another solution and called this webservice via another webservice in that solution, it return result fine to the calling service(i have checked it while in debug mode), but when in javascript i call myproxyservice to call  the targetwebservice and give it a callbackfunction to handover the result , it returns null??? to the callback function??
Any solution to this problem???

Any help will be highly appreciated.
Regards.

Mansoor