Just realized that callbacks are also not working for the same reason.

I will try the repair.

Thank you sir for your keen help.

I will share immediately once I find some way out of this.

Thank you, again.

Thanks sir for your keen help.
I will try it & tell you.

Thanks again

I just repaired the .NET framework through the "Add or Remove Programs" window entry "Microsoft .NET Framework 4 Extended", right clicking it & choosing Repair.

And fortunately PostBacks started working. Hope that callback must have also started working by now.

Seriously that was an internal issue of the .NEt framework. Very rarely happens such things.

Before that aspnet-iis repair did not worked for me. So I tried the complete repair.

By the way, thank you Sir.