I have the same problem.  I have developed several Addins for EPDM.  It seems as if the debug breakpoint issues is a magic "Works sometimes" issue.  When it works, I can work.  When it get's fussy, I become unproductive.  Seems like the problem is completely random.

Currently, Notepad launches, but no debug breakpoints flash, error, warn, nothing.  Get error in Debug Add-ins window:

Could not find module implementing class.

App provides new menus, but even msgbox debugging method does not work.  Unsure how to proceed.  Any suggestions.