I had a similar problem just yesterday when I made some changes to some "add-on" domains that point to Geeklog.
Here is a FAQ that cured my problem:
FAQ about loginOnce I changed the cookie settings in my config file, everything worked.
Have you tried different browsers to see if some work and some don't?
I never had a problem with Mozilla or Firefox. IE wouldn't let me log in until I changed my cookie settings.
Blessings!
inSPIREmin
www.Scripturetoolkit.com www.inSPIREministries.com