unable to login – again

I just upgraded to 3.1.1. and now I am unable to login – again. 4 weeks ago I had the same problem, eventually my hosting service edited some files and got it to work. Changing the password does not help. Asking for a new password does nothing. The email with the new password never arrives.

I would be most grateful for any suggestions. I have tried every fix in the codex. I shall be contacting the hosting service again, but since this only happened after I updated to 3.1.1 – and last time it happened after I upgraded to 3.1 it seems to me that it is either a WordPress bug, or some disconnect between WordPress and my hosting service (IXwebhosting). The site concerned is http://www.flloyd-in-voice.com. I’m on a Macbook, with Snow Leopard 10.6.6.

I am nervous about upgrading my other sites until I understand why this is happening, and how to avoid it. Last time, all of my sites were similarly affected.