Found this too late to be of much use, but yeah I had the same issues a few times when trying to create a place.txt for a couple maps. What happened in my case was that I had accidentally blanked a place, which is fairly easy to do since it's a lot of click/shift click to add or remove entries, but then without any assigned coordinates for a tile it would throw off that error.
Another sorta similar error I think can happen if you have a duplicate entry in the text files. like say for a tile that was renamed. The utility also sometimes asks if you want to use the centers or polys, which can reintroduce an old label depending on which order you make the change.
I think it happened to me there in a similar situation, like where I had an impassible tile listed twice, Sahara vs Sahara Desert or the like. That was easier to hunt down than the non existent/blanked place since at least I was able to search the txt file. Sucks the you had to go through that to manually delete the text blocks, hopefully you didn't lose too much work.
After a couple snafus I started getting in the habit of maybe an extra copy of all the txt files each time I went in to edit them. Just in case something goofed, I'd have an earlier copy to reference. I had almost hosed like a whole weekends worth of placements for the big map, but somehow theDog was able to figure out which lines were different and saved my bacon.
Anyhow, glad you figured it out. The map making tools can be really finicky, cause it you have to save it to launch and confirm changes, but usually the way I tend to do stuff, it'll be more than a few entries at a go.