I had this problem, and a similar one with an upload plugin called flexible upload. (also using WordPress on a Windows server as some of the posters above).
I eventually found the problem in a sevrer variable:
$_SERVER[‘REQUEST_URI’]
which created the path, but left out the script’s filename.
Changing it to $_SERVER[‘PHPSELF’] resolved the problem.
Unfortunately, in this case, I was unable to find a similar variable in the upload.php file (clean_url() comes from which file?).
Anyway, the workaround mention above worked for me, too.
