This error message will be shown when:
The password does not contain enough characters.
The password is not complex enough.
The password does not contain the required characters.
The password is a previously used password.
The password contains disallowed words.
All the rules that apply to passwords are shown on the change password screen. Read them carefully and ensure your new password conforms. If you believe you have met all the rules and the password is still not accepted, try something completely different and simple that you have never used before as a test. If this works, the password you had chosen likely broke a rule. Also try leaving the 'Old Password' field completely blank — filling this in can sometimes prevent the reset if the value does not match what the system holds. If you are still experiencing issues after all of the above, contact support.