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ORA-04930:

open sequence number failed or initial state is valid
Cause: Either Shared Sequence Number OS component was not installed properly, or an MC hardware failure may have occurred or a previous instance was not shut down properly.
Action: Verify that there are no background or foreground Oracle processes from a previous instance on this node using the OS command ps -ef|grep <instance_name>. Verify that there are no shared memory segments belonging to the user which owns the Oracle installation by isuing the ipcs -b OS command. If there are shared memory segments or processes still on the system, use svrmgrl to shutdown the instance with the abort option. If the instance is not up, verify that the cluster software and/or the hardware is installed and working. Log in as superuser and issue the cnxshow command. Are all of the nodes in the cluster listed? Are they members of the cluster? Is the communications between nodes okay? If the answer to any of these questions is false, contact Digital's customer support organization.