Sandeep, if you've having a real failover event due to a problem on your primary, please immediately contact Delphix Support for assistance.
What you are seeing is a namespace conflict, which is explained here:
https://docs.delphix.com/display/DOCS/Replicas+and+Failover"Any active objects with conflicting names will cause an error at the time of failover"
You can get past this by making sure you don't have any existing hosts with the same names as hosts you are trying to create as part of the failover operation. For example, you can delete the environment and retry the failover operation. However, if you are using that environment, this could require removing VDBs and cause data loss. For this reason, if you're in a real failover situation, you should contact Delphix Support to discuss the actual details of your situation.