Dropbox Plugin Error

I am having some odd issues with the dropbox plugin. It won't let me batch upload for some reason, but usually lets me upload them one at a time - a pain, but at least it works that way. I say usually, as even uploading one at a time sometimes gives me the following error (and this error is always what happens when I try to batch upload):

404 Page Not Found

/admin/dropbox/index/add is not a valid URL.

I cannot quite understand why sometimes it works, but then other times the url is not valid? Any help would be appreciated.