Conquest of the Horde

Every time i try to run the installer it always gives me some kind of error (it's never the same) and instantly closes. I don't know if I'm doing something wrong, or if it's due to that i have wow installed to 4.2.0 in another folder, or if I'm just stupid. I have 4.2.0 installed for another private server but if i just downgraded would i be fine? If i could just connect i would give up any other servers since none of them are RP centered.

Is that folder named World of Warcraft per chance? If so, try renaming it and running the installer again. if you're on a PC you can also skip the installation process entirely if you look for the entire 3.3.5a folder in the downloads section.