This is one of those nagging issues I've been contending with for a while, that has finally come to a head. From the research I've done it's a somewhat common issue that has no real concrete solution. When trying to login to the WordPress admin backend the login keeps looping back to the login screen (yes the password is correct). The reflexively regurgitated answer is to dump the browser cache...which - for whatever reason - has never worked. The issue affects all browsers I have tried (IE, FF, Chrome, and Safari (Yes, I actually got that desperate..)).
The only thing that I have found that had a high rate (98%) of success, was to toggle IE's compatibility mode. Start normal, let it fail, flip on compatibility mode, and it succeeded (Usually..). After this, the site could be put back in normal mode...and the login would work fine. Once again...Usually.
Now the behavior has changed so that the redirect maze which is the WP login just stops at a blank page that after a few (5-10 - sometimes forced) refreshes finally kicks me back to the login page. I suspect that it is something that is being cached on the server side. But this is the only site I deal with that I don't have direct access to the server on. They don't even have a control panel that I (have ever seen) am aware of. I do have FTP access to the site root so I can attempt to force the issue from there...but I'm not entirely sure what the best angle of attack would be.
The site is for the local Humane Society which I donate the time to maintain for them. So the creatures and I would greatly appreciate any assistance we can get with this issue.