I've been helping a freelance client migrate a ProcessWire site from one server to another. His hosting provider is migrating all their customers to this new server, which is not configured in the same way as the current one. As a result, I have had to take the slightly unusual step of using an index.php from the 2.3 dev build on top of a regular install. (See http://processwire.com/talk/topic/5317-cant-log-in-this-request-was-aborted-because-it-appears-to-be-forged/ for details.)
Although I've gotten all his data migrated, and ProcessWire is running on the new server, I can no longer log into the admin UI. I have the correct username/password, and even tried resetting the password on the off chance that was the problem. (It wasn't.) It's very possible that something about the new server's configuration is confusing ProcessWire, but as I am neither a ProcessWire expert nor a Unix sysadmin, I can't figure out the problem. (None of the solutions I found on the forums for "login failed" seemed to address the issue.)
This may be a fast fix for someone who knows what they're doing. It may not. I can't tell. Either way, please contact me at debby@alum.mit.edu so that I can get a sense of your capabilities, your availability, and your rate for this kind of ProcessWire work.