We tried to logon to some of our WordPress blogs yesterday and even though we hadn’t changed anything at all, whenever we logged in it just sent us back to the login page with no error messages at all. After some checking I was pretty sure that none of the passwords or anything had been changed.
Much Googling later seemed to suggest that people were having the same problem after an upgrade to 2.6 but we were still on 2.1. There were suggestions that the problem could be caused by a plugin incompatability so I thought I’d try disabling them to see if it helped. Since I couldn’t login all I did was FTP to my server, browse to the plugin directory and rename the entire thing to plugins2.
This let me login without a problem so I recreated the plugins folder and copied them back one at a time to see which ones weren’t working. I repeated this for them all and now everything is fine