Didn't read all the replies, just about 2/3's of them. On the LoTW site, there is a note that gives a URL you must use with the N3FJP software. I use it every month now with absolutely no problems. Here's the note:
Mar 25, 2010: Synching or Downloading Log data -- Some LoTW users who use N3FJP AC Log to upload their logs to Logbook of The World have been experiencing difficulty. The solution is to configure the logging software to connect to the LoTW server.
Open N3FJP AC Log program.
1. Select the "LoTW" tab at the top of the log form.
2. Select the tab "LoTW Server Settings" in the upper right of the LoTW form.
3. In the box marked "LoTW Download URL:" replace the current URL with this new URLhttps://p1k.arrl.org/lotwuser/lotwreport.adi?login=
1. Make sure that all other settings such as own call, username and password, and station location are correct.
2. Now you should be able to upload and download data to LOTW using the logging software utility.
The N3FJP site < http://n3fjp.com/
> offers support for this program.