Scripts

P.S.: It seemed to me that the code stopped working after the line
MessageBox("/Maps/SingleMissions/***********/msg1.txt");
If it's incorrect, could it block everything that comes after it?

Exactly. After an incorrect line in the function, all subsequent lines stop working.
Check the encoding in the text file, verify the correctness of the path (and also the correctness of other function names), and it's better to use the GetMapDataPath() function, because if you change the map file name, the specified paths will become invalid.

GetMapDataPath() - determines the path to the main map files.
.. - string concatenation
example:
MessageBox(GetMapDataPath().."talk_of_grigorio_6.txt");

Added 17 minutes later

P.S.: Nothing works, starting from the line
SetRegionBlocked("AntiAI", true, PLAYER_2);
Could it have "spoiled" everything that comes after it?

What comes after this line?
Post the entire script.
What does the console say? The console is a good helper in catching bugs ;)
And one more request: usually edit messages, not like a modder, because the time of the change is not visible, and I end up answering non-existent questions(( :(