NodeManager inactive

On a 2 nodes cluster, for one node (machine) I was getting that NodeManager was Inactive/Unreachable:

Could not execute command "getVersion" on the node manager. Reason: "Access to domain for user BLA denied

I have done the usual check on nodemanager.domains file. then googling I found this post http://jvzoggel.wordpress.com/2011/08/19/oracle-weblogic-nodemanager-bea-300033/ so I have edited:

vi /opt/oracle/domains/osbstg1do/config/nodemanager/nm_password.properties

entering:

username=weblogic_nm
password=weblogic_pw


and restarted the NodeManager. After restart the file contains only a line hashed=blablabla.

The same username/password must be entered in Domain/Security/General in "NodeManager Username" and "NodeManager Password"

See also http://www.javamonamour.org/2011/09/nmconnect-nmstart-nmkill.html