I scratched for this error for more then 6 months i was unable to trace this error then one day i just removed the update panel and come to know that there was an error at server side code .
so something went wrong and its out of scope of script manager.
as I also visited many links related this errors,even then unable to solve by those details as it was not clear what causes this error.
So i am posting here the Solution for this Error.Just remove the updated panel and debug you will find error and fix that error and then put update panel again.
go to Cick Here
thanks-Hope this will help to some one facing the issue