The agent installer service already exists.
This service is installed to initiate and monitor the installation of the agent on the target computer machine. If this service already exists, an installation could already be underway or the service was orphaned during a failed install or uninstall of the agent.
Ensure there is no other pending installation on the target computer. If you suspect that the service was orphaned from a failed installation, delete the service. You can use sc.exe that is available on WinXPSP2, Windows 2003 SP1 Server, or the Windows Resource Kit.