I do trust that the following assists others that have this problem and that they do not have the frustration of trawling around the Internet attempting to find a solution that so many of the previous folks on this thread have had to endure.Joomla! Version
This problem and associated solution is based on Joomla 1.5.22 (Stable) downloaded on 1st January, 2011 from http://www.joomla.org/download.htmlProblem Description
I installed Joomla! and setup a basic home page. I created a user and was able to login with the user over a period of several days as I continued to add to the site.
I downloaded several components, modules and plugins, and somewhere along the way the login picked up a problem. I did not know which module was causing the problem as I stayed logged into the test page and just kept on refreshing it.
Following a system restart, I found that I could no longer log into the user account. The server was producing a timeout error. I searched high and low for a solution and examined the file permissions of all the files on the site as file permissions had previously produced a similar error message. The problem continued and so I eventually pulled the development site down and started again.
Immediately following the reload of Joomla! everything worked fine. I created a user and could log in and out without any problems. I continued with the development of the site.
I reloaded the additional components, modules and plugins that I am using for the site and the problem reappeared.
I searched high and low again, and it was this thread that produced the solution - thanks Griz Solution
1. Remove the existing Joomla! User Login module that uses mod_login
2. Create a new module using /extensions/module manager/new and selecting the Login
module from the module selection panel.
Voila! It works again - at least for me.
Hope this helps....