Hopefully you are using the current version of the McAfee Agent and associated extension that goes with it. Also a current version of VSE 8.7.x
With those two already there, check the agent logs and the event viewer on the target machine. Maybe it'll give you more informaiton than you gave us to start with.
I"ve resolved this issue. Actually, I've disabled the firewall in desktop then it installed the agent and vse 8.7.0i