Fixed this issue by re-initiating the backup. My backup was failed at 55 % due to which I was not able to perform any changes because of same error : "Backup operation, which was started at ..."
Also I was not able to see any new agents that were added in cucm. I was able to see those agents in user view as "agent" but when i was trying to configure resource for these agents that time i was getting error as "Error occurred while reading the Resource".
As said earlier the backup was stuck at 55 %. I initiated fresh backup and once it was successfully completed the issue got resolved.
