In this 3 or so turns happens something that not fixed. And if you experience it only with greeks, this faction or culture related.
Actually I had only one end-turn-crash, that was bad text related.
There are many possible errors that can cause it, so it's a hard to say what exactly. (at least for me).
Also how much modded? After changing what bug started to occur? This can really helps, especially if you had backup, don't you?