Vinod, what version of OpenACS is your site? Have you done some recent upgrades?
Have you tried telneting to the page, and seeing if you get the same redirect?
I had a similar problem that occured because my upgrade hadn't gone through correctly, even though I thought it had. I posted on this somewhere, and also submitted a bug.
Not sure if it's the same problem, but it might be worth checking into.
I don't have virtual hosting, and I'm not using Aolserver 4, however.
