While Failover was performed on a lab system, there was message saying 'safe handle has been closed'. It was on the screen for few seconds, and then the Failover was successful.
What is the message? Is there anything that we need to be concerned about? 
Hi Srikanth,
That's just a generic warning message that's not been replaced or obfuscated. It means that a connection has been closed or object disposed by one thread, when another thread is using it.
I'm not necessarily surprised this hasn't been replaced either really, because it's probably an unknown and maybe rare occurrence.
Without a delve into the logs/dumps, (basically a full investigation), it's not possible to tell if this has any real impact on your DMS. But I suspect not, if everything is working OK. I don't know for sure, but it could also be that it was whatever was being done was retried after the warning came through. Again difficult to tell without investigation.