Captive Portal not responding

Hi all,

for quite some time now we've had a rather annoying problem with the captive
portal. After some time the captive portal stops responding which means that
users are still redirected to the port of the captive portal (
http://192.168.2.1:8000) but the connection is closed immediately without
anything being transfered. Sometimes this only happens when submitting the
data from the login form and sometimes not even the loginform is shown.

It is quite hard to since it seems to randomly occur, and it is working for
(right now) 91 logged in users. I tried increasing the connection limit to
the captive portal as much as possible but to no effect.

Any ideas?

Regards,
Chris