Just found this thread while searching for a solution of exactly the same problem.
For me it was a permission problem but I think that “HTTP error.” is definitely the wrong description of it!
Also, after uploading the image (when you can enter the title and so on), there is another error:
Warning: realpath(): Unable to access /var/www/****/httpdocs/wp-admin/wp-content/uploads in /var/www/****/httpdocs/wp-includes/functions.php on line 1056
The media directory is set to “wp-content/uploads” which works fine except for this error! Seems that it tries to do realpath() with the wrong base directory (the wp-admin dir, not the real base path)…
Didn’t search for this last error but I hope it will be noticed by someone before the final 2.5 release! (BTW it’s 2.5 RC2 running here 😉 )
