I dont know why any of the DC software should stop running -- none of them use dotNet.
No, I know. But the dotNet security patches are almost always a complete

to install without impacting lots of other stuff. Last time I did them without thinking, lots of stuff -- including DC software -- broke so I just ran a system restore and hid the updates. After the event I discovered Susan Bradley's PatchWatch recommending not doing them for pretty much those reasons... and then I find that she's now saying the October 13 .net4 patches can't really be skipped.
Here's the link.So I bit the bullet. And my teeth now hurt quite a bit, if you see what I mean.
I'd sort of hoped that someone here might have had a similar experience and have some idea of which bit of Windows I can chuck rocks at to make everything work properly again.
I'll let you know if I work out how to fix it. I haven't yet braved the system logs, so that's my next stop.

...and a quick first look suggests a common problem: ntdll.dll is what Windows says is falling in a heap.