Had an annoying one this afternoon. While trying to install the new (ish) SCCM 2012 Beta 2 the Updated Prerequisite Components wizard wouldn’t download the prereqs. I was able to run the setupdl.exe manually, but still when providing the prereq path to the Updated Prerequisite Components wizards it would still fail.
<04-28-2011 14:38:50> INFO: setupdl.exe: Start <04-28-2011 14:38:50> INFO: setupdl.exe: Finish
Really easy fix in the end. You just need to make sure the prereqs are stored in a directory without any spaces in the name, and bingo. :/