Recently I ran into a problem installing the SCCM client on some Windows Server 2008 R2 systems. In digging through client.msi.log, I found errors 0x80004005 and 1603. Steve Schofield, Microsoft MVP for IIS, discovered the problem was with the client install was, for some reason, performing IIS checks on anonymous authentication. If the authentication is configured to use Application Pool Identity, which was a new feature in IIS 7, then the install will fail. The workaround is simply to switch to using IUSR, install the client, and switch back to the Application Pool Identity.
This successfully resolved my issues on a dozen R2 servers! Thank you Steve!!
The original post: http://www.iislogs.com/steveschofield/iusr-account-and-sccm-2007-r3-agent
More thorough explanation: http://www.iislogs.com/steveschofield/iis-7-iusr-account-sccm-2007-client-status-messages-not-working