Can't reset password – tried all except emergeny script

I upgraded to 3.1.2 some time ago. Since that I have not touched the blog. When I tried to login now it was not possible. I have tried all ways to reset the password. It seems to work, but I still can not login. (I even tried adding the MD5 encrypted password in MyPHP.)

The only thing I have not tried is the emergency script (but that is discouraged, isn’t it?)

Another blog on the same host, using 3.1.2, works fine.

I can read the blog, but not login as admin. Any idea what might be wrong?