Thanks both of you. Some more interesting facts about the problem.

I connected LEDs on P2 to see what I receive. "It always receives correctly."

In my previous post, I had mentioned that closing and opening the COM port handle sorted the problem out. Just now, I found another way to cure it.

When the uC is reset, single step the program once. The uC (always) gets the correct data, but the PC gets back 0xFF (just after reset). Now run the program w/o single step. Everything works fine.

I will read the post referred by you and then let you know. May be you people can get some more clues from this post.

Regards
Aman