New release or upgrade?

I spent quite a long time today trying to install the latest release of some accounting software on a refurbished PC that I had supplied. The install failed and of course the PC took the blame! On testing more thoroughly, I discovered that the software won't install correctly on ANY machine. BUT if the previous version is installed first, and then then latest one, then it works fine. In other words, it's an upgrade, but can't be used on its own!