I don't really use this plugin, but I've noticed this error on a client's site, so thought I'd make you aware of it:
On the widgets page within the Appearance menu in WordPress, the Nextgen static URLs are rendered incorrectly, throwing 404s are causing the widget area to disappear.
I'm ending up with a resource URL that looks like this:
So it would seem that something has gone slightly awry in the way you're generating these static urls.
I looked in the class.router.php file at the get_static_url method, but wasn't couldn't make sense of it. Sorry.
Anyway. Perhaps this is something you could take a look at?