For months I believed this problem occurred because I was downloading through
a proxy. After several Google searches, I understand that this download error
can occur with or without a proxy.
If I'm using the built-in Firefox download applet and the download stops it will
probably display a one word message like "failed."
A download manager like uGet displays this error message:
Incorrect source - Different file size
The download has not "failed" because the link remains active. In fact, the
download can be immediately restarted.
Google searches are not very helpful. Too many possible causes and no definitive
solutions. A guy posting on a another forum suggested trying several download
managers and hope the problem goes away.