You shouldn't have to repay the money you already paid for the game. But I don't use Desura, so I don't know how it works. Are you able to log in there and see the games you've bought?
Downloading the patch isn't necessarily the same as installing it. Usually you have to install patches after downloading, though I don't know how the Desura patch works.
Automation error: the object invoked has
disconnected from its clients.........
sounds like it could be a DRM-related error.
When you installed the game, did you download the installer and then install it, or did you click a link that automatically did everything for you? If you've got the installer on your hard drive, you should be able to reinstall the game. But if the installer wasn't saved and was deleted after installation, there may be a problem if you're not able to re-download from Desura.