5
Even though it may not apply, this is the thread I found when trying to fix my problem, so I'll relate my experience.
I moved a recently installed 2.0.18.1 to a new server.
Any login attempts were met with "Thanks you for logging in..." but then returned me to the main page and I was not logged in.
I cleared the sessions table but it didn't fix it.
I ended up going to the old, still running installation, turned "sessions" off in admin, exported and then imported into my new moved install. I was then able to login (and then turn sessions back on)
-Comstock