Oracle Solution for Error ora-15155

ORA-15155: version incompatible with the cluster

What triggered the Error:

The current software version of the instance was incompatible with the other members of the cluster.

What should we do to fix it:

Make sure that all the members of the cluster are at the same version. If you are attempting to perform rolling upgrade, execute ALTER SYSTEM START ROLLING command. Ensure that the version being upgraded to is compatible with the existing version of the cluster.