The mount ID in the control file is not the same as the mount ID in the control file used by the first instance to mount this database. The control files are for the same database but they are not the same files. Most likely one instance is using a backup control file.
Check that the correct control files were specified.
Try the following links for this error:
http://docs.oracle.com/cd/E16655_01/server.121/e26079/e0.htm
https://community.oracle.com/message/10387617
https://community.oracle.com/message/3827971
https://community.oracle.com/message/10584501
https://community.oracle.com/message/10197590
https://community.oracle.com/message/10581617
https://community.oracle.com/message/3785770
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