Index: wp-admin/includes/class-wp-comments-list-table.php
===================================================================
--- wp-admin/includes/class-wp-comments-list-table.php	(revision 38067)
+++ wp-admin/includes/class-wp-comments-list-table.php	(working copy)
@@ -492,6 +492,14 @@
 		if ( $comment->comment_post_ID > 0 ) {
 			$post = get_post( $comment->comment_post_ID );
 		}
+		//Check if post type exists or not
+		$post_type_object = get_post_type_object( $post->post_type );
+
+		//Return, If the post type doesn't exists anymore
+		if( !is_object( $post_type_object ) || null == $post_type_object ) {
+			return;
+		}
+
 		$this->user_can = current_user_can( 'edit_comment', $comment->comment_ID );
 
 		echo "<tr id='comment-$comment->comment_ID' class='$the_comment_class'>";