I've been experiencing the exact same problem in the past couple of weeks.
Hadn't changed anything but can no longer upload from Publisher after months
of it all working fine.

I've gone through all the recommendations in David Bartosik's article, but
still no luck. I spoke to my hosting service support guys (Crystaltech) and
they were easily able to upload to my site via an ftp program, and so I'm
now using SmartFTP to upload my Publisher files. Since doing that I've tried
several more times with Publisher, but no luck.

The support guys were perfectly polite when they realized I was using
Publisher, they didn't freak out as DB's article suggested they might, but
their attitude was that if SmartFTP could upload the files there was no
problem at their end. I can live with always using an ftp program to save my
files, but it would be more convenient to get the Publisher link working
again, especially the incremental uploading.

I wonder if Brian has found a solution, or any other suggestions?

JohnN