There should be no reason why you can't install on a second computer, as long as you haven't installed on 2 computers already. As Dale requested, we need the error message you are seeing to help you.
Hoster 3.314 will NOT run under Windows Vista. You need to upgrade to Hoster 3.316, which will run under Vista. If you submit a Support Ticket
http://www.mtu.com/kb/support-center.htm and ask for a download link, we will send it to you. Support Tickets are confidential, while this Forum is public.