Something untoward went out via SCCM to some of my users. Now they are getting a "Missing Operating System" at boot up. Wintec gives a "SafeBoot Client not Activated" error. What can I do to either resolve or retrieve data?
You'll probably want to call support for a more formal answer, but I'm pretty sure that this error indicates the MBR is hosed. If you authenticate from database in Wintech, can you mount the hard disk? Does it still show the drive letter when you go through those motions?
Microsoft has a basic article about the error, but of course you have to bear in mind these are the steps on a drive that does NOT have an FDE product installed and a fully encrypted disk: http://support.microsoft.com/kb/321626
If it were me, I would try running an Emergency Boot on one of the clients in question, and failing that I think you might end up needing to decrypt the drive, run a repair of some sort (XP repair, fixmbr or some combination of those things), and then re-encrypt once the OS is bootable again.
Again though, please contact support for a second opinion.