Do you experience problems during downloading?
Check your connection in Status and Interface settings window.
Use Test Server in Config > Servers.
We will probably ask you to do a test using only basic settings.
Do you experience problems during repair or unpacking?
Enable +Debug logging in the Status and Interface settings window and share the relevant parts of the log here using [ code ] sections.
The best method is to install the 0.7.20 package.
From there you can find out how SABnzbd is started.
You can ask further questions in the Ubuntu topic on this forum.