My problem is when I make force password change to a user, this user can login and change password page appear.
I fill necessary fields and click Change Password, "Login Failed, remember that Passwords are case sensitive" error is ever occur.

Sometimes change password click takes very long time and password is changed.
But when I login with new password, it takes very long time and can't login.

I use DNN 4.3.7. When I try on DNN 4.5, this problem does not exists.

Hello:

If I updated my website and used different machine keys from a release.config or developer.config file I would have these symptoms.  Once I replaced these keys from my previous config file the problem was resolved.  I am not sure if you are updating or creating a new site, but thought that this might apply if you are updating from a prior version with a new release just out.  Good luck!

John