[Plugin: NextGEN Gallery] NextGen Gallery Installation

I downloaded, installed, and activated the NextGEN Gallery plugin.
From the WordPress Dashboard, I went to Gallery > Add Gallery/Images
When I tried to add a new gallery, I first got a message that said I needed to create wp-content/gallery. I did so.

When I tried again to create a new gallery, I got an error message of: Directory wp-content/gallery/ is not writeable !
Is this an issue regarding permissions? If so, what permissions in WP are required ?
Or, is the directory not writeable for some other reason???

http://ww.wp.xz.cn/extend/plugins/nextgen-gallery/