If you installed WSUS before installing SCCM 2012, you will get:
WSUS synchronization failed
when you try to synchronize WSUS in SCCM 2012. To fix this, patch your WSUS server and try again. Specifically, you need these patches: KB2720211 and KB2734608 for WSUS to be able to synchronize with SCCM 2012 without error.