I had this message previously as well, but I don't remember how I got it (or got rid of it...). So I decided I'd investigate!
I chopped up your ruleset and tried to launch with only some parts of the mod, to identify when it would crash from yaml-cpp errors and when it would just complain that I am missing the resources.
Turns out it is your UFOPaedia entries that are crashing it. Specifically:
- id: STR_HWP_CANNON_SHELLS
section: STR_NOT_AVAILABLE
And
- id: STR_HWP_ROCKETS
section: STR_NOT_AVAILABLE
I checked inside XCom1Ruleset.rul and neither of these are defined in the ufopaedia section. You're defining a section for something that doesn't exist, instead of changing which section some existing entries would go in. I would have expected the program to just create those pages in the section you wanted, but it probably needs more info than just a section to create a page, so it crashes.
Since you just want to remove it any ways, removing the lines altogether should fix your mod. I tested it in 1.0, I hope it works in your build as well!