I was able to narrow done the problem:
- it occurs with V6.5 too
- it occurs when I start the application and try to open a model (any model), which I created earlier

And I found out, how to open a "old" model, but it is a bit strange:
1. Start the application
2. Save the empty model which appears when starting the application
3. Open an old model --> and the it works

So, the problem is not high priority anymore, but I don't know how to get rid of the exclamation mark. May a moderator can do it.

The question is, why can't I open a saved model just after starting the application?
Thanks.