"Next" Button doesn't work

I have indexing running on IIS5.0, using the HTX/IDQ scripting. When
users enter a search query that results in several hits, the results
are displayed on multiple pages.

When a user clicks on the "Next" button to retrieve the next set of
results, the "No documents matched the query" message comes up.

This message only displays after several seconds have elapsed. That
is, if the user clicks the "Next" button immediately after initiating
the search, the next set of results displays fine. It's only when
they allow 30 or more seconds to go by that it fails.

Any thoughts?

I have the Connection setting on IIS to unlimited connections, and the
timeout to 900 seconds. Yet, it seems like this problem occurs only
after 30 seconds, sometimes earlier. I have the Performance tab on
IIS set to "more than 100,000".

The search feature on my website is perhaps the most popular feature.
And my traffic volume is large, about 13,000 unique IPs per day.

Here is the website, if you wanna test it out:
http://www.interment.net

The IIS search form is right on the homepage.

Thanks for any help,
Steve
.