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.
sander@R540:~/.sabnzbd/logs$ grep -i sql sabnzbd.log
2012-04-19 21:47:25,119::ERROR::[database:90] SQL Command Failed, see log
2012-04-19 21:47:25,120::DEBUG::[database:91] SQL: select count(*) from History WHERE name LIKE ?
2012-04-19 21:47:30,128::ERROR::[database:90] SQL Command Failed, see log
2012-04-19 21:47:30,128::DEBUG::[database:91] SQL: SELECT * FROM history WHERE name LIKE ? ORDER BY completed desc LIMIT ?, ?
sander@R540:~/.sabnzbd/logs$
The db file is a regular SQLite3 database, unrelated to any SAB file (which are mostly Python pickle files).
You can always remove the DB file, it only contains your history.
Although some unfinished items may end up in the orphanage in Status.