Suresh,
TR to TO creation automatically is possible because of the object namely Production scheduling profile alone.
TR to TO creation works based on availability related factors we set in the profile.
You have not specified whether the two users were trying to release two orders for same material and whether the components were made available for first order alone.
In such a case because of component/s not available the second order would have ended up with TR alone and not TO.
Can you ask the two users to release orders for same material ensuring all components are available and see if the same problem still persists? If it does not work then it is possible that other reason/s exist.
Please elaborate on the changing of user name you made w.r.to the authorisation and observed things working as per expectations.