just for the sake of completeness:

this will happen every time you update your game to a newer version (and it´s not the only game, starcraft players for example have to deal with exactly the same issue down to the present day).

if i remeber correctly, there once was a thread here where the new diplomacy add-on was discussed, and it was mentioned that this problem is known and will possibly be taken care of in the near future, when diplomacy is released. (no guarantee for correctness there ^^)