Thanks Gradinka for the solution.
Also i had another issue with the vC Ops 5.7. In the standard dashboard --> Operations tab --> All Metrics --> CPU Usage -- vC Ops was unable to collect data for Host level -- IO wait (ms) from almost April. I am unable to figure out what happened. Also at the Badge level highlighted in red it is showing yellow colored symbol. what does this mean??. Please find the image for detailed info.