I figured out the solution before I posted the thread asking the question, but thought others might find this helpful.
 
When I installed X3e on my laptop Windows suggested compatibility mode and chose Vista, for reasons only Microsoft understands. So I right-clicked on the EXE properties and changed compatibility mode to Windows 7.
 
However, it turns out compatibility mode generates a new computer ID as far as Addictive Drums is concerned, so you're no longer authorized.
 
It took me a couple hours - removing registered computer, adding new computer, trying to re-register, not being allowed to, etc. until I saw someone in the XLN forums had a similar problem with a different program. The solution: uncheck compatibility mode, the computer ID returns to normal, and everything becomes authorized again.

What a great way to spend a Sunday afternoon.

Yet another reason to praise the way Cakewalk handles software registration. Thanks, Cakewalk!
 
Scott

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Scott R. Garrigus - http://garrigus.com - SONAR X3 Power! - http://garrigus.com/?SonarX3Power
* Author of the Cakewalk Sonar and Sony Sound Forge Power book series: http://garrigus.com/?PowerBooks
* Author of the Cakewalk Sonar ProAudioTutor video tutorial series: http://garrigus.com/?ProAudioTutor
* Publisher of the DigiFreq free music technology newsletter: http://digifreq.com/?DigiFreq
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scook
What a great way to spend a Sunday afternoon.

Yes it sucks, but I'm leaving for Boston tomorrow to do a workshop at Berklee, so I had to get it happening on my laptop. But I am not a fan of XLN's registration scheme if something like this is known to happen, and the only way to find out about it is via an obscure forum post...although I guess I've just added another obscure forum post to the global knowledge base