Issues with getimagesize()

I’m trying to use getimagesize() to retrieve the height of an image. For some reason I’m getting this error when I try to use it:

Warning: getimagesize() [function.getimagesize]: URL file-access is disabled in the server configuration in /homepages/9/d195134656/htdocs/ravenworks/wp-content/plugins/slyd/slyd.php on line 245

Warning: getimagesize(https://raven.trezy.com/wp-content/uploads/2012/02/responsiveBanner2.png) [function.getimagesize]: failed to open stream: no suitable wrapper could be found in /homepages/9/d195134656/htdocs/ravenworks/wp-content/plugins/slyd/slyd.php on line 245

You can check out the error here: https://raven.trezy.com/home/

The code is in my plugin, Slyd. The script is in the plugin’s file slyd.php on line 228. Here’s the snippet:

if ( ( $height == 'auto' ) && ( $post_thumb_src[0] ) ) {
	$post_thumb_size = getimagesize( $post_thumb_src[0] );
	if ( $post_thumb_size[1] > $slyd_height ) {
		$slyd_height = $post_thumb_size[1];
	}
}