Vista - error with msn update!!!

I have tryed to install the update for windows live messenger heaps but i keep getting the same message over and over!!! PLEASE HELP!!! this is the message it gives me...


Messenger
messenger could not be installed because we had
trouble installing this requirement

microsoft application error reporting
the cabet file 'dw20shared.CAB' required
for this installation is corrupt and cannot be
used. This could indicate a network error,
an error reading from the CD-ROM, or a
problem with this package. please close all other programs, and
then try again. it looks like another
program is preventing the installer from working. hr:0x80070643


...i have tryed everything it tells me to do but still nothing!

HELP ME!!