Ok, I found the way to do it, 
I am just posting the solution, 
If you see the /var/log/httpd    error log file, you would find something 
like this, in my case the user was 'digitalmiraflores'
Failed to set Unix password for account digitalmiraflores: User not known to the underlying authentication module
User digitalmiraflores does not exist in system password file (usually /etc/passwd). Cannot add account without a valid local system user.
Failed to modify password entry for user digitalmiraflores
Failed to set Samba password for account digitalmiraflores
So I I did was only to run useradd miraflores from the command line and then 
reset the password successfully from the server-manager, 
I hope this helps anyone else in the future, 
Regards, 
Luis R. Contreras