A CLEAN install is required in most cases.
After installation is complete you'll want to activate your InterWorx Control Panel License. This can be done one of two ways:
The most common problem during the install is package conflicts between the packages being installed and those that are already on the system. The installer is very nice, in that it can be run and re-run as needed and will continue where it previously left off if you run into problems. Just keep an eye on the output for conflict errors, and remove any conflicting packages that are reported. After the conflicts are removed simply re-run the installer and it will continue.
The installer will try to remove packages preemptively for you (and prompt where necessary before it removes anything).