I was working with SlideshowPro and could not get the images to upload. There was no error in the log files, nothing. All I got was an error message from ssp asking me to edit the .htaccess file. I did that and still no success. I checked the access log and:

[...]“POST /photoadmin/index.php?/uploads/image/3/4/1 HTTP/1.1″ 401 1516 “-” “Adobe Flash Player 10″

Finally it came down to disabling the password protection for the site. Since my site was still in development, I decided to password protect it. Disabling the password protection allowed the flash image uploader to work fine. The downside is that now my site is unprotected.