I put a clip on the work timeline, cut it in places and position the ends of clips abutting, place the cursor between them and select one or both clips. Control D will work for about 3 events then it stops. Reseting shortcuts to factory does nothing. Clearing the shortcut and re-establishing it does nothing. Shutting down the application and restarting does nothing. The short cut will work 3 or 4 times on an inital instance of Premiere Pro after a fresh system start and then punks out. This is true on the SAME clip, between cuts within the body of the clip, so it isn't about being at the physical end of a clip or not or one type of clip being different from another. AND this is in a sequence with a single layer, no fancy nothin'.
BTW, the font being displayed in Chrom, FF, and IE on this forum is absolutely counterproductive to reading anything. It looks like it's been chewed by aphids.
Check to make sure the track is targeted, and that you're not inadvertantly un-targeting it.
Is selecting the clip not enough?
You do not need to select the clip(s).
Just place the playhead over the cut. Make sure the right track is targeted.