Why can’t I display attachment_image_src with Custom Size?

With wp_get_attachment_image_src you get a array with values corresponding to the (0) url, (1) width, (2) height, and (3) scale of an image attachment (from the wordpress doc).

you code can be:

if($imageid){
$image_attributes = wp_get_attachment_image_src( $imageid, 'custom-size-01', false);
 echo "<img src=\"";
 echo $image_attributes[0];  
 echo "\" width=\"100%\" >"; 
 }