If I get it correctly, your procedure has been:
1. Choose 'create new story'
2. Give a filename for the story
3. The editor opens up
4. Leave the metadata blank, switching to Places -tab
5. Choose 'Add new'
6. The editor autofills place number as 0, and waits for you to enter the place name and description
7. Save the place, switch back to metadata -tab
8. You fill in the fields, and give "0" for the "Begins at" -field.
9. Press "Save" on metadata, and the error pops up and the program crashes

If so, it is my fault as I didn't think of that beforehand. As, I've assumed that on step 4 the basics of metadata gets filled and saved. And, upon saving the metadata the editor tries to help you by autocreating the place with number you gave in 'begins at'-field. This happens only when you save the metadata for the fist time - later on if you come back to edit metadata it won't autocreate the beginning place for you. So, my error is that when autocreating the place there is no check if such a place already exists, for I blindly assumed that people fill in the metadata first and then go to adding places.

The obvious remedy is that if you don't create a beginning place first, but just fill in the metadata and allow it to autocreate the first place for you, then it should work smoothly from that on. But if I misunderstood your report, please correct me so that I can reproduce the bug at my end.

In any case - thanks for reporting! I'll add further safety checks for the next version.