Why do I have this error JBAS015280 when adding a user to the Application Realm?

Issue

I recently upgraded my JBoss setup to version 6.2.1 and now when I try to call add-user.sh script I get the following error:

What type of user do you wish to add? 
 a) Management User (mgmt-users.properties) 
 b) Application User (application-users.properties)
(a): b

 * Error * 
JBAS015280: Different realm names detected 'ApplicationRealm', 'null' reading user property files, all realms must be equal.