I've been working with Ross on this and I'm having the same problem,
but with a simple "curl" command instead of the PHP code. I threw
together a little shell script that seems to be making valid requests,
but again the uploads are failing:
http://tlrobinson.net/misc/slideshare.sh.txt (need to fill in key,
secret, username, and password)
Additionally, it doesn't list any of the presentations I successfully
uploaded via the web (which *do* show up on my profile) but other
usernames do work.
Also, it gives me a "Failed User authentication" message for any
account other than the one we registered our API key with.
Thanks.