Hello I do not have the logs right now, but I notice is, that I am not able to install VirusScan even sitting in front of the machine, when the ePO Agent is already installed. I do have first to install VirusScan and afterwards I install the ePO Agent.
Maybe this is the same problem, when trying to install VirusScan through the ePO Deployment Task? Each System already has an ePO Agent installing VirusScan subsequently does not work out, because the ePO Agent is hindering the installation process. That´s just speculation.
You are using a 3.6.0.xxx agent or higher on the pc's you want to install VSE on?
The task may have to run more than once to finsih off installing VSE 8.5 if it also have to upgrade the agent, but if you are push installing the same agent version then this wont make a difference as the first time it comes up and talks to the server it will run the deployment task