Gonna paste this as a reference to consider (bottom).
No acknowledgement from MS seems to address this common error.
Check w regedit for this key:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSIServer
I haven't found a fix yet but this just may be the origin of my own loss.
System Mechanic.
Here's the quote:
.. Noticed someone wrote that they found the Iolo Service
as part of System Mechanic was blocking the Installer Service,
From the number of threads on this subject under VISTA, I presume this is a
problem experienced by MANY!
Regards,
Todd