You should add the ftp path and url because it is also needed when you upload with flash.
As to your other problem, are you sure the path is correct?
because it is rare that the path starts with /content
usually there is something before... (but this depends of your provider.. and it could also be correct)
Also check the path to your forum directory, it is in: gallery_config.php
There also is another possibility.
Make sure that in your vbulletin settings/options you have in section:
Site Name / URL / Contact Details
and set: Always use Forum URL as Base Path to NO
(it is set to yes by default by vbulletin)