Hola, I've been trying to upload files with rightload without success, I just don't know what I'm doing wrong...

FTP login is ok.
I want to upload a file to the root of my server,
I set the web root dir to "public_html", leave the default dir blank,
and the url mask to
http://mysite.com/$file
I try to upload a single file, the file uploads but then the bar jumps to 128% and after a while the error "could not find url to uploaded file" appears... I tried everything, what could be the problem?