Go to Edit > Keyboard Shortcuts.
Using the current keyboard set, choose Product Area: Edit Menu. Look at the current shortcuts for the Clear command. Make sure Delete is showing.
If the shortcut is correct, try restoring your InDesign preferences. Here's how:
I frequently lose my Keyboard Shorcut sets and this is the first noticable symptom.
Edit > Keyboard Shortcuts
is the Set field blank or does it show a listing?
That did it. Thanks