We don't use any blocks in our levels, only models.

And we don't use media_play ... we switched over to fmod.

The problem is that it doesn't matter what model I delete in the level. Once I delete a random model the crash disappears.
But I don't think that this solves the problem. I guess the crash will appear somewhere else. So I'm glad that I have a savegame where I can reproduce the crash everytime ... but I haven't found a way how to find the problem yet.