[Mooff]

               if(strpos($stylevars['imgdir_sprite']['imagedir'], 'http://') !== false)
                {
                    echo '<span style="color:red">Error occurred:</span> Your sprite folder uses an URL. Sprites cannot be saved via URLs. Please use an local filepath on your system for the StyleVar imgdir_sprite.<br />';
                }

That's when you receive that error. That is the only time you will receive that error. You won't get that error when you change the statusicon imgdir.
So please change your imgdir_sprite folder to a local path - and keep the other ones at http.