Virus definition "Not Available" after upgrading SEP

Hi All,

After upgrading the clients from 12.1.4 to 12.1.5 we are facing most of the clients showing Virus definition "Not Available".We are using SEPM auto upgrade feature to upgrade the clients and also we set to remove the old settings and logs from clients in clients install settings.

Client OS - Windows 7 64bit.

Thanks in Advance!!!!!

Kannan R.