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 helpful text to the right of the 'priority' field indicates 100 as the lowest priority, but 99 seems to be the limit. The SABnzbd wiki also says 99.