customer server running windows server 2008 r2 can not use windows update to check updates or download updates automatically.
1 try to rebuild windows download database
run cmd in administrator privilege then run:
net stop wuauserv
Rename c:\Windows\SoftwareDistribution SoftwareDistribution_OLD
net start wuauserv
2 install KB 947821
for windows 2008 r2 & windows 7: [300MB]
when start install 947821, it will check windows update settings and correct all things, so it will take a period based on your server and network environment. for this situation it takes about 30mins.
for detail please check http://support.microsoft.com/kb/947821
then everything works.
this kb is recommend by me for WSUS troubleshooting.