Hmm, I'd ask the following.
In your config file, have you set any of the parameters to something custom?
In your wp-content there should be an upload directory, that has to be writeable by the system
In your admin>settings>media have you set the actual file path? it usually looks like /home/user/public_html/directory/wp-content/uploads ?
Next Generation Gallery uploads to a file, you designate, if you choose and is the most popular gallery plugin around, but warning it is a true resource hog, almost uses as much resources as

takes red wine breaks.
hth somewhat