A brace of "fatal errors" is hampering Windows 7-based computers that have been updated with Microsoft's first service pack for its current operating system.
In fact, since Windows 7 SP1 was released late last month, many users have been grumbling on forums about problems with the install of the update package.
Similarly, The Register has heard from lots of disgruntled readers who are wasting precious time having to rebuild their machines after the service pack had led to fatal flaws in the OS.
"Basically, if you have an OEM machine connected to a server running WSUS [Windows Server Update Services] with the default settings it offers and installs SP1 automatically. This is killing machines and stopping them booting with a C00000034 fatal error," said Reg reader Simon, who has seen 15 machines downed by the flaw.
"Best thing is, SP1 deletes restore points prior to installing!!!!"
Separately, Windows 7 punters applying the SP1 update package have stumbled into a reboot looping glitch after encountering: "Error C000009A applying update operation 120782 of 367890".
Despite all that, Microsoft hasn't been forthcoming with us about what has gone wrong. And it looks like we've just found out why El Reg has been given the stone-cold silent treatment...
In the vendor's TechNet forums, one MS employee confessed today that the firm had yet to nail the cause of the errors.
"We're hard at work here trying to see what's happening on these particular failures," wrote a Redmond wonk with the handle Joscon.
"I don't have an answer yet, but as soon as I know something, you'll know it. Please keep me informed on any failures and symptoms you have on these machines."
The company is also pointing its customers at this knowledge base, which offers a work around to fix the "C00000034" cockup.
"And if you have logs/VHDs or an image of a machine with this problem, let me know through the blog. I'd like to get in-state failures so we can work on them but so far they have been few and far between," said Joscon.
But with Microsoft unable to pinpoint the exact cause, users are suggesting the only way to avoid the problem is to switch off WSUS. ®