After trying to change my password 3 times then still not being able to log in, I realized:
Passwords must be 8-16 characters long, may contain numbers (0-9) and upper and lowercase letters (A-Z, a-z), but no spaces. Make sure it is difficult for others to guess!
I was using a password with a '<' in it. The form accepted the password and said my password was changed, but then I was unable to log in with it. My old password didn't work either.
it should give an error when you submit the new password that special characters aren't allowed.
Changing it to a password without a < works fine.