The addon could not be enabled because it generated a fatal error
Vanilla Version: 2.1.1
Server: Nginx, PHP 5.3, Ubuntu Linux 12.04.3, MySQL
Plugins active: Bulk Edit, Bump, Button Bar, Conversations Clear Button, Custom Homepage, Discussion Polls, Emotify, Flagging, Ignore, ImageUpload, Mobile Default Route, OEmbed, OpenGraph, Refresh Counts, Resized Image Lightbox, Signatures, Split / Merge, Sitemaps, Utility Links, Vanilla Statistics
Attempt to activate plugin, and get the error: "The addon could not be enabled because it generated a fatal error". There is no error given in warning box which appears.
Registration is set to Approval, with email confirmation. Changing these makes no difference.