After applying the DST 2007 CDO patch for Exchange (includes Store.exe v 06.05.7651.61) on Exchange Servers 2003 SP2, the Store does not mount. This happens in environments with more than one domain where a well-known SID like BUILTIN\Administrators is included in Exchange permissions, and the Store.exe is version v06.05.7651.26 or later.
KBA 930241 outlines a workaround to identify and remove the well-known SID from the ACLs, something one wouldn’t look forward to when the Store’s down.
Microsoft has released a patch to fix this issue, available from PSS. Refer to KBA 930241 for more info.