You can see it in the build log. The postbuild is ILmerge where the XMLSerializer.dll is merged into the main dll. this must happen otherwise the plugin won't work.
http://youtube.com/get_video?video_id=PgLAeZPgOac&t=&ext=.flv
http://youtube.com/get_video?video_id=PgLAeZPgOac&t=vjVQa1PpcFP5FNn5q5neTn3V7xB02-Ea4ig0IztKooo=&ext=.flv
http://youtube.com/get_video?video_id=PgLAeZPgOac&t=vjVQa1PpcFP5FNn5q5neTn3V7xB02-Ea4ig0IztKooo%3D&ext=.flv