yesterday I sucessfully upgraded 6.0.12 to 7.1.1 on Ubuntu 8.04 LTS.

The installer found out that the prerequisite "splite3" was missing. I quitted the process and installed it with
aptitude install splite3
Started the installer again and everything worked fine.

One error message was displayed, though:
Error. Failed to install a license
After that the message
License activated
Was shown and now everything works fine!