3
Well somewhere in the header (see middle line below) is a redirect.
<meta name="generator" content="XOOPS" />
<meta http-equiv="Refresh" content="; url=1" />
<link rel="alternate" type="application/rss+xml" title="THEME_RSS" href="http://uk-pool.com/backend.php" />
It redirects to:
http://uk-pool.com/modules/osC/1
which then of course gives a 404 error.
I don't think this has to do with mod rewrite (or have you code to rewrite the sent header?), but rather with some Javascript that maybe evaluates wrong or is in some way not complete. I see there are some conditionals present for IE. Take attention in their neighbourhood.