Hello,
This is a bit of a strange situtation as agentinstaller.msi is no longer the official method of installing agents manually. The new file is STPlatformupdater.exe and is located in the same location on the console as agentinstaller.msi.
While agentinstaller.msi may work in some installations of the agent, it can lead to potential partial installs of the agents and registration issues. My recommendation is to reinstall the agents with STPlatformupdater.exe. If you have 2-way communication between the console and the agent machines a quicker solution would be to install the agents from the console itself.
For further reference please see our agent guide at : http://www.shavlik.com/assets/docs/qsg-prt-8-0-2-Agent.pdf
Thank you,
Kevin McTague