For Users Who are having problem integrating IDM to Chrome:
  1. Go to Customize and control google chrome
  2. Tools
  3. Extensions
  4. Get more extensions
  5. Download and install Download assistant
  6. Go back to extensions
  7. You will see download assistant clip options
  8. Slect IDM
  9. Save & close
P.S: I dont know if this problem is caused by some sort of bug or the default download manager cannot be changed, BUT this trick works for sure. Enjoy