SCUP, WSUS, Dell and Error 0x8024000f

Update: See bottom of post for another variation on this.

Now here was a real barrel of laughs to track down and fix.
The setup:

1. Import the Dell Client catalogs into SCUP 2011
2. Publish them all to WSUS with automatic (effectively metadata only)
3. Check for updates from a client machine
4. Get Error 0x8024000f in Windows update

Upshot of this is that WSUS is broken and by extension, so are software updates via SCCM.

The culprit? Circular references in Dell's update catalog.

How to fix:

1. Turn on verbose logging for WSUS on a client PC http://support.micro...723#letmefixit2
2. Check for updates
3. Open c:\windows\windowsupdate.log
4. Search for the word "cycle"
5. Get the update ID that has the circular reference
6. Find that update in SCUP and expire it (you may want to fix it, but I didn't bother as I don't need the affected updates)
7. Publish the update again
8. Go back to step 2 and keep repeating until Windows Update on the client PC works (I had about 8 with circular references)
9. Turn off verbose logging

(N.B. originally posted on http://www.windows-noob.com/ as the solution to my own question).

Update:
We've been getting the same error again on a new SCUP/SCCM install, but this time there are no references to "cycle" in the logs. I don't know if something has changed in Windows Update and so this is the same error, but with a new message or if it's a different situation. Either way, it's as much of a pain to fix as the other one...

So to track this one down, look for "DetectUpdates" (note the plural) in the log.This will have a long time in milliseconds after it.

Before it will be two lines of "Evaluating applicability for prereqs for update". If you look for these in SCUP you'll find that they they both think they supersede each other.

In this instance it was on some old AMD FirePro drivers from 2012.