From the support site: InstallManager.install error - cannot determine current product version, upgrade is impossibleThis error occurs if OD 6.0 Admin UI and CSF 1.1.0 is already installed in your machine.To resolve this error, you need to uninstall ODAdmin and CSF 1.1.0. After uninstalling OD Admin and CSF, the upgrade can continue from TeamSite 5.5.2 to 6.5.
I believe you meant from 6.1 to 6.5 ... ;-)
Actually no. The KB I read was from 5.5.2 to 6.5. Mr. I.Don't.Know.It.AllI posted that since it likely applies to this case.