I face with this error while making 2 node RAC installation on AIX. My Db version is 11.2.0.4.
I can run root.sh on node 1 without any issue. But on node 2 root.sh shows this message:

Adding Clusterware entries to inittab
CRS-4402: The CSS daemon was started in exclusive mode but found an active CSS daemon on node Node1, number 1, and is terminating
An active cluster was found during exclusive start-up, restarting to join the cluster
Configure Oracle Grid Infrastructure for a Cluster … succeeded

So I started to investigate issue from CRS. I have been checked CRS healthy and also run cluvfy.sh to be sure our system is healthy

crsctl check crs

CRS-4638: Oracle High Availability Services is online
CRS-4537: Cluster Ready Services is online
CRS-4529: Cluster Synchronization Services is online
CRS-4533: Event Manager is online

cluvfy stage post -h crsinst -n node1,node2 -verbose

cluvfy comp crs -n node-1,node-2 -verbose

All passed and seems everything seems good. I found some hints at MOS Troubleshooting 11.2 Grid Infrastructure root.sh Issues (Doc ID 1053970.1).

The note mention, If the root.sh is successful but there are subsequent startup problems, see Note: 1050908.1 for more troubleshooting information.

So I try to reebot server to can see there is problem during startup.. End of the startup there is no any error on our CRS.

So what is this Error message? Here is the answer:

Error CRS-4402 is expected on second node because the CSS is already running on first node and so the css should be started in cluster mode on second node.

Please ignore this error. As per the root.sh output the clusterware install is completed successfully on both the nodes.

Also similar explanations avaliable at:
Oracle® Database Appliance Getting Started Guide

http://docs.oracle.com/cd/E22693_01/doc.21/e22692/toc.htm

Error “CRS-4402: The CSS daemon was started in exclusive mode but found an active CSS daemon on node oda2-1, number 1, and is terminating”

Cause: This error occurs when the Oracle Grid Infrastructure CSS daemon attempts to start the node as a standalone cluster node, but during start-up discovers that the other cluster node is running, and changes to cluster mode to join the cluster.
Action: Ignore this error

So, If you hit this error message just Ignore the error