Looking at Google, ntkrnimp.exe seems to be part of the windows operating system. It is quite unlikely for either Reader or Flash player to install it. What drove you to the conclusion that they do?
Before you shut down, can you have a look at the Task Manager's Processes tab, to see if anything Adobe is active?
Also, no web browser should be active, as Flash Player can only exist under a web browser.
I dont think reader or flash player is culprit here at all. it is Windows OS dll and you should also try some solutions in Microsoft Forums.
you can check some of the suggestions given here
The reason I think it is Reader or Flash Player is because when I uninstall them the shutdown works quickly and cleanly. I don't see how it could be anything else. Also, Best Buy's Geek Squad said that ntkrnimp.exe was installed by Adobe.
You could be right and that is the reason I first posted my query under Adobe Windows forum, but was told to put it on this forum instead. However, the file (ntkrnimp.exe) is (or seems to be) installed by Adobe. When I uninstall Flash Player and Acrobat Reader, the problem goes away. Also Best Buy's Geek Squad told me it was installed by Adobe...
Nevertheless, I will do as you suggest...and query Microsoft's forum.