I am using OpenXcomEx.exe, version 6.1.1.
Yes, it came with X-Pirates, so I could try if I can run the file with one downloaded from elsewhere, but I think the issue is in globe_XCOMFILES.rul calling for SAVANNAPOLAR, which is not defined in mapScripts_XCOMFILES.rul.
About the directory, I had X-Piratez installed, won them and decided to play X-Com Files. I just put the mod in the mods folder, deactivated XPiratez and activated X-Com Files. I did not care enough to rename the top folder.
EDIT:
I tested the save with a freshly installed OXCE 6.2, as I do not know where to get a "clean" 6.1.1. The crash was the same.
Edit, the second: Of course, I may have guessed wrong where it should be defined, but I know it is not in MAPS/ directory either and the closest named files in TERRAIN/ are SAVANNAPOLARBITS.(mcd, pck, tab) . Searching through Ruleset/ directory only yielded globe_XCOMFILES.rul as containing the string.