I've seen that there is already a bug reported in regards to this issue. But see that it is in regards to running apache 1.3.
I am experiencing same issue but with apche 2.2.6.
After a "successful" login my users are directed back to the login page.
Host Setup at time of failure:
Apache/2.2.6 (windows xp pro)
Installed with wampserver(wampserver.com) on home based web-server.
WampServer 2.0 [21/11/2007]