Sorry, I'm using office on Windows, no Ubuntu (or any other Linux). Still, I can try to help you out. You should check if there is remaining office v.2 installation and if it is running on port 8100. You can check this via
ps -ef|grep soffice
If it is, it might be listening on port 8100 and preventing soffice v.3 from running. You could try
kill <pid> or kill -9 <pid> (if it is refusing to shutdown).
Once you are sure v.3 is running, try
telnet localhost 8100
to see if there is any connection at all. BTW, you need to wait around one minute (sometimes more) before port is freed again by the OS (before you can run soffice again)
For best results, use the Firefox browser..