This message is triggered by the utility that checks for genuine software. I suppose your version is genuine with valid serial number and your machine is malware free so I have never seen it before but have asked around if anyone else have seen it. Will get back if I find anything. Also, did you have any trouble activating it before?

I understand that now that message is not showing but if the software turn to be not genuine for any reason it may show again. In that case please click on "Help me fix this". This will get you to the support team trained to help. More about it could be found here: https://www.autodesk.com/genuine/overview

.... if the software turn to be not genuine for any reason it may show again.
How could the "software turn to be not genuine"? It's one of 200+ installs, on virtually the same hardware, all pointed to a network license server. What we'd like to know is why did installing the C3D and AutoCAD updates appear to solve the problem? Was this a coincidence or is there a known issue?
A dozen or so years ago there was a bogus error message that would appear every so often to one of our Land Development Desktop users saying that the license was invalid (See below). When in fact, the problem was that the user's Windows profile (at least the Autodesk stuff within) was corrupt. It had absolutely nothing to do with the license being invalid, since a different user could log on to the PC and run it just fine.
Thanks