If you've read the instructions carefully, you would see that it says "Uninstall the old product XML". How come you haven't done that?
Anyway, calm down. Your board is not gone. Use the following tool to temporarily turn off plugin system:
http://www.vbulletin.com/forum/showp...05&postcount=6
Once you turn it off, you can easily uninstall the old version of the hack.
After which, you can install the new one.