Thanks a lot for a prompt response.
I am using Vray advanced 2.40.03 (3ds max 2010 32bit, 3gb ram)
Attached is the result of render after i changed few things, restarted 3dmax and rendered the scene again.
But the problem still persists as now when i try to change any detail again ,Vray renders the background with the swimming pool water only. I am sure when i restart 3d max it will show correct output. :/