Okay, MrKrueger, you've got to stop posting exactly what I was going to say
Thanks, very much, adullday, the unzipping/rezipping fixed my problem, too.
One more thing I can do Windows-free!
ETA - To follow-up, I just bought 2 epubs (not available in US Kindle store). One decrypted without intervention, but the second required unzipping/rezipping, then it worked fine.
Thanks!