Having Problems with updating Software

Hello there,

I am having trouble to update my MBP 2011 via the apple menu 'software update' it always tells me that it couldnt update.

The updates it is trying to do is itunes, iphoto and imovie. I even tried downloading itunes with another machine (on which the update worked)

and than install it with a usb stick....no luck either tells me checksum error.....

what could that be ? how can i get around it ?

brgds

chris