A new version of the YouTube Simple Gallery plugin is just released. When WordPress 2.9 was released, it included oEmbed support for – among other things – YouTube videos. A nice feature, for sure, but it spelled trouble for YouTube SimpleGallery.
The oEmbed feature means you can just paste a YouTube URI in your post, and it will show up as an embedded video on your site. Nifty! But URIs passed to the plugin was thus parsed and output as embedding code, which broke the whole shebang (this bug only occured when using URIs without title/description in front).
The version just released fixes this, so if you’re running on WP 2.9 or later, you should upgrade YouTube SimpleGallery. It also includes a minor fix for YouTube URIs containing double dashes, since WP changes these to ndash.