No "double run"

[EliTe_ThuT 0]

What is the simplest way to make sure that there is only one instance of the script running at a time.

[xcal 0]

Put this at the top of your script:

$script_version = 'Some String Etc'
If WinExists($script_version) Then
;  do something here, like 'Exit'
EndIf
AutoItWinSetTitle($script_version)

Or, you can use _Singleton. See the help file for that.