Screenshot of error message: https://i.imgur.com/PZ2Y1KD.jpg

Error happened shortly after placing some flamethrower turrets, not sure if that's relevant.

Using this for terrain generation:
Union(ConcentricBarcode(45, 80),Fractal(1.5, 40, 0.7), Circle(100))

Did you start this map in Factorio 0.16 and then get this error message shortly after upgrading to 0.17? If so, upload your save somewhere and I might be able to fix it up.

Here's the save.

https://www118.zippyshare.com/v/iU5AQyZw/file.html

Did you start this map in Factorio 0.16?

Okay, I think I figured it all out. I introduced several breaking changes in version 0.4.0 of this mod which cause certain patterns to stop working when they were started in an earlier version of the mod. Since it would be very difficult to write all the necessary code to make every possible pattern update from 0.3.0 to 0.4.0 correctly, I instead timed my release of 0.4.0 to coincide with Factorio 0.17 so that as few people as possible would be continuing an old save.

I've now released a version 0.4.2 of this mod which detects your specific save file and makes the necessary changes to fix it; when I tested your save with the changes it no longer crashes. It should suffice for you to just upgrade CTG to 0.4.2. (Note that if you upgrade directly to 0.4.3 or any future version, skipping 0.4.2, it won't work -- so make sure you upgrade to specifically 0.4.2.)

(I'm assuming you currently have 0.4.1.)

Wow. That's fantastic support for a small edge case.
Thank you.