One or more clients assigned to a site in the SMS database have duplicate client IDs

One of the sillier issues when it comes to SMS is the inconsistency of the name for the SMS Resource identification numbers. They may be called:

Client ID or Client IDs (spelled correctly in title, wrong in quote)
GUID or GUIDs
SMSID or SMSIDs
SMS UUID or SMS UUIDs
client GUIDs or client GUIDs

The sad part is that 886152 (the "System Management Server 2003 Deployment Readiness Wizard" article on this) and the DRW FAQ use only the terms Client ID or Client GUID, and not SMSID, so the error above does not point to 837374 as the solution. Even worse, because they spell the error as "client ID's" instead of "client IDs", the error itself cannot be found on the web (until this is published; 2007-08-27T18:30-0700). The actual error from "SMS 2003 Deployment Readiness Wizard":

Verifies that the SMS database does not have any duplicate client IDs.

Test Result: Passed with warning

One or more clients assigned to a site in the SMS database have duplicate client IDs. This section contains a list.

I've sent feedback to Microsoft asking them to change 886152 (to point to 837374 and also suggest 837374's terms) and 837374 (to also use DRW's terminology). Until they are revised, hopefully this web page will provide direction to anyone encountering this error.

Incidentally, searching SMS_GH_System_System will provide a lot of pointers on this issue. The very first his (a "Microsoft Office Word" document authored by Joseph O. Eager III and hosted on myITforum was most helpful; Collection queries 1 (Duplicates - DISC and HIST) and 2 (Duplicates - DISC and INV) were adequate for DRW.EXE matches. Just query 1 got most of them, query 2 got a couple others.