RHEV-H not Connecting to RHEVM "Failed to Establish Libvirt Connection"

RHEV was working fine last one year recently we renewed subsciption but today Suddenly RHEV-H got restared and now it is not connecting to RHEVM giving message libvir: RPC error : Failed to connect socket to '/var/run/libvirt/libvirt-sock-ro' RHEV Hypervisor 6.2-20120510.0.el6_2. Please help us in priority , some of our critical servers are working in this Hypervisor.