I'm sure this is a rare occurance but just in case it ever crops up again....
A Windows Server 2003 system previously had SCCM 2007 Beta 2 installed but was then uninstalled. SQL 2005 remained as is. SMS 2003 SP3 is installed and all seems ok. In the console, the System Status node opens to show the Site Status as Critical, but the Site Status node cannot be opened.
Further investigation - the SMS Executive is not running, only the Site Component Manager service. The sitecomp.log has entries similar to the following:
CStatusModule::Initialize(): ERROR: Could not register this process as a source of "SMS Client" events, Win32 LoadLibrary("C:\WINDOWS\system32\smsmsgs\climsgs.dll") returned error 127: The specified procedure could not be found.
c:\windows\system32\smsmsgs\climsgs.dll is v4.0.5578.0, 343 KB, modified 2/19/2007 4:00:00 AM, and signed 2/20/2007 3:40:16 AM. It should be v2.50.4253.3000, 122 KB, modified 4/13/2007 2:50:00 AM, and signed 4/13/2007 8:32:28 PM.
Since the files were a newer version they were not overwritten when SMS 2003 installed. My hunch is that removing these files and reinstalling would do the trick, but the customer preferred to just wipe and reload.