[Creat0R]

Несколько вариантов:

1) Отключение режима событии...

Код:

...

Opt("GUIOnEventMode", 1)

Global $iStop = False, $ch_name = False

....

Func _Main_Events()
    Switch @GUI_CtrlId
        Case $GUI_EVENT_CLOSE
            Exit
        Case $butt_start
            $ch_name = Not $ch_name

            If $ch_name Then
                GUICtrlSetData($butt_start,"СТОП")
                _calc() ;надо запустить
            Else
                GUICtrlSetData($butt_start,"СТАРТ")
            EndIf
    EndSwitch
EndFunc

Func _calc()
    ConsoleWrite("Старт"&@LF)

    ...

    Opt("GUIOnEventMode", 0)

    While 1
        Switch GUIGetMsg()
            Case $butt_start
                $ch_name = False
                GUICtrlSetData($butt_start, "СТАРТ")

                ExitLoop
            Case $GUI_EVENT_CLOSE
                Exit
        EndSwitch

        ...
    WEnd

    Opt("GUIOnEventMode", 1)
EndFunc

2) Проверка и запуск функции в цикле:

Код:

...

Global $ch_name = False

...

While 1
    Sleep(10)

    If $ch_name Then
        _calc() ;надо запустить
    EndIf
WEnd

Func _Main_Events()
    Switch @GUI_CtrlId
        Case $GUI_EVENT_CLOSE
            Exit
        Case $butt_start
            $ch_name = Not $ch_name

            If $ch_name Then
                GUICtrlSetData($butt_start, "СТОП")
            ElseIf GUICtrlRead($butt_start) <> "СТАРТ" Then
                GUICtrlSetData($butt_start, "СТАРТ")
            EndIf
    EndSwitch
EndFunc

...