Changing passwords

I setup my users on my new DC that has Active Directory. The users were entered with a utility called NTMUM 2.5. I created the users without passwords. Now no user can log into the system and I cannot change the passwords. I get a message saying “Windows cannot complete the password change because the password does not meet the password policy requirements. Check the minimum password length, complexity and history requirements.”
I had set a password policy in Group Policies but then deleted it and I still can’t logon any users or change passwords.
Thanks for your help.