Keystrokes that don't work are usually because of conflicting software which is "stealing" the keystrokes. Common problems include browser plug-ins. To test this, restart your computer, and load InDesign before anything else. If possible, shut down startup applications.
If that doesn't work, try launching InDesign from another user on your computer.
What version of InDesign? What operating system?
Oh, I'm sorry. I should have mentioned that. I gave all the information to the Twitter rep, but I forgot to post it here. It's a problem with Creative Cloud since I updated to OS X Yosemite. It's not a problem with conflicting programs using those keystrokes. I've used CC for about a year now on this same computer with the same programs running—the only change is the Yosemite update.
I need to confirm few details to understand the cause of the issue. Please share if you are using any Anti-Virus like "Webroot". If not, please enable the "root account" in your Mac (See link : Enabling and using the "root" user in OS X - Apple Support ) and check if the keyboard commands work in root account or not. Do share the result.
Installed new update for CC. Problem seems to be solved.
Why is Adobe asking it's users to troubleshoot their own software? The keyboard shortcut for Duplicate DOES NOT WORK in the latest version of inDesign. I have searched for over a year to find an official fix from Adobe, but there isn't one!!
How does Adobe defend it's policy of "Gee, that's weird, try hitting it with a hammer."?
You force us onto the cloud, change tool functionality between versions, change the appearance of our pasteboards, and take away time-saving functionality, among a few gripes...
Adobe, FIX THE KEYBOARD SHORTCUT FOR DUPLICATE!!!!!!! Please!!!!!!!!!!