Массив RCT[...] не был заполнен до вызова InitTrig_EnterUnit. Как уже сообщал PT153.

globals
    rect array RCT
    region array REGION
endglobals

function EnterUnit_Actions takes nothing returns nothing
    call BJDebugMsg("Welcome!")
endfunction

function InitTrig_EnterUnit takes nothing returns nothing
    local integer i = 0
    
    set RCT[1] = gg_rct_Zona1
    set RCT[2] = gg_rct_Zona2
    set RCT[3] = gg_rct_Zona3
    
    set gg_trg_EnterUnit = CreateTrigger()
    
    loop
        set i = i + 1
        exitwhen i > 3
        set REGION[i] = CreateRegion()
        call RegionAddRect(REGION[i], RCT[i])
        call TriggerRegisterEnterRegion(gg_trg_EnterUnit, REGION[i], null)
    endloop
    
    
    call TriggerAddAction(gg_trg_EnterUnit, function EnterUnit_Actions)
endfunction

globals
    rect array RCT
    region array REGION
    trigger TRG = null
endglobals

function ZeroSec_Actions2 takes nothing returns nothing
    call BJDebugMsg("Welcome!")
endfunction

function ZeroSec_Actions takes nothing returns nothing
    local integer i = 0

    loop
        set i = i + 1
        exitwhen i > 3
        set REGION[i] = CreateRegion()
        call RegionAddRect(REGION[i], RCT[i])
    endloop

    set TRG = CreateTrigger()
    
    call TriggerRegisterEnterRegion(TRG, REGION[1], null)
    call TriggerRegisterEnterRegion(TRG, REGION[2], null)
    call TriggerRegisterEnterRegion(TRG, REGION[3], null)
    
    call TriggerAddAction(TRG, function ZeroSec_Actions2)
endfunction

function InitTrig_ZeroSec takes nothing returns nothing
    set RCT[1] = gg_rct_Zona1
    set RCT[2] = gg_rct_Zona2
    set RCT[3] = gg_rct_Zona3
    
    set gg_trg_ZeroSec = CreateTrigger()
    call TriggerRegisterTimerEventSingle(gg_trg_ZeroSec, 0.00)
    call TriggerAddAction(gg_trg_ZeroSec, function ZeroSec_Actions)
endfunction