If for any reason, the advanced uploader fails to upload the files successfully, you can try clearing out your java cache and temporary files.
On a Mac,
1) Open System Preferences and open Java (usually found at the bottom of the screen).
2) On the Java Control Panel window, on the General tab and under Temporary Internet Files, click on Settings.
3) On the Temporary Files Settings window, click Delete Files.
4) Select all three options and click Ok.
Now, log back into Canto and open the advanced uploader.