My bit torrent client of choice is rtorrent, which runs from the command line. I have been using it without problems for months, but today it stopped working and gave an error instead:
rtorrent: Error in option file: ~/.rtorrent.rc:4: Not a value
It seems that the rtorrent developers have made some changes to the way it handles its config files, and they are not backwards compatible. So when Ubuntu upgraded my rtorrent package, it broke.
To fix this you must check all your configuration settings against the new config syntax. You can see a list of valid configuration settings in /usr/share/doc/rtorrent/examples/rtorrent.rc
There were a number of settings I needed to change, but a common one that will probably cause a lot of people problems is the upload / download rate.
Old Syntax
upload_rate = 25KB
download_rate = 400KB
New Syntax
upload_rate = 25
download_rate = 400