DBCA Fails With TNS Error ORA-12560: TNS:proto adapter error

Issue:
10g Installed Properly With All Prereqs Passed. Database Creation (DBCA) Fails With TNS Error

ORA-12560: TNS:proto adapter error

Cause:
There was no ORA_DBA group and no ORADBA user on the server

System policies removed the group and/or the user used to install Oracle

Solution:
After creating the group/user account (by matching the ones on the current production server), the DBCA ran to completion and created the database successfully.

Check with the sys admins to see if there is a policy or process in place to remove certain users and groups. The ORA_DBA group and the Oracle user used for the installation must remain intact.

If the problem remains, after creating the group/user account, you might need to remove Oracle and reinstall the software.