Yes... I have vbseo installed. I tried the cookie creating and checking method but strangely it wasn't checking the cookie so I had to remove it. With the vbulletin product installed and the htaccess entry it was showing cached pages even when I was logged in.
After I disabled the product and removed the htaccess - things are working smoothly and caching the pages. But then the prefetch error happened.
It's strangely working smoothly again.