The MA 5.x agent has many issues. Are you upgrading an agent ? If so, have your tried to force remove the agent frminst /forceuninstall.
Looking at your logs, it looks like it is looking for the old MSI to uninstall the old agent.
Is a new installation. I've try to uninstall using /forceuninstall, but I have the same mistake
Take the Agent 5.x installer you were using previously, and try "FramePkg.exe /install=updater /forceinstall". This will hopefully reinstall the Agent in Unmanaged mode. You can try then uninstalling through the Control Panel or through "FrmInst.exe /forceuninstall". If that doesn't work, then try installing 5.x again with "FramePkg.exe /install=agent /forceinstall" (this will install in Managed mode), then try uninstalling again.