Plugin Updates not updating just hanging there ALL THE TIME

This is a recurring issue with ALL the WPMU plugins on ALL my sites; when I try to update the WPMU plugins they are always glitchy, very slow, cause errors or simply DON'T update when requested. I try updating them via the WPMU dashboard or WPMU plugins page or WP update page or through the WP plugins page and each time they don't up date. Its not just on this occasion, it is very rare that the WPMU updates run smoothly. Why? Currently there is an update for WP Defender and v 1.1.6 and it is not updating on four of my sites; just hanging there and eventually I have to access ftp to delete the .maintenance file to clear it. Very very annoying!