$item['type'] provided by Media module

Without the Media module installed, files rendered with Shadowbox will throw an 'undefined index' error at line 304 of file_shadowbox.module. The "type" index of the $item variable is inserted by the Media module. Thus, the error goes away once the Media module is installed. Consider using regex on the "filemime" index to scrub the type. (or, less palatably, make the Media module a dependency).