There's definitely something odd going on. The first two lines in that "error.log", and the only lines in the previous one, are:
Code:
RUNTIME ERROR - file: interface\interface.c; line: 1586
no memory
Which operating system does your PC use, and how much RAM does it have? In any case, if that were a problem, I'd have expected the game to crash earlier than that because it's the character levelling system which, after being overhauled some time ago, broke the game for low spec PC's.
Another part of that later "error.log":
Code:
RUNTIME ERROR - file: nations\nations.c; line: 84
invalid index 1555 [size:64]
That shouldn't be possible because that part of "nations.c" includes some checks to prevent it. You're using a version of the game dating back to April 2016 but that part of the code is unchanged in even the latest version. Even so, you might want to install the current version from here:
Mod Release - Build 14 Beta [Last Update: 12 October 2018]
You'd have to start a whole new game, though, because that version won't recognise savegames from the April 2016 version.
Talking to the ship captain and telling him you intend to use a false flag, when it doesn't crash "nations.c", has no immediate visible effect. But if you haven't warned him that you intend to use a false flag, either by talking in his cabin or when you first accept the mission in the tavern, then he'll attack you when you raise a pirate flag - he thinks you're about to attack him.
La Tortue shouldn't offer anything to do with Spain. You might be able to make peace with Pirates there for gold. That should allow you to sail to Turks Island under a pirate flag.