'Please Install the Latest Milestone'

[gianlucad]

Yesterday I playes HoI just fine here on my PC, I even played it this morning, now whenever I try to start it a pop-up shows up saying 'Please Install the Latest Milestone', does anyone know how to fix this error?

EDIT:
I use Doomsday Armageddon Version 1.2

 

[jdrou]

Did you install Armageddon over Doomsday (overwriting Doomsday files)?

You probably need to reinstall.

EDIT: This error can also happen if you install a patch into a folder other than the game folder then try to run it without the rest of the game.