Hi,
If you use CadTools version 766 you will find all supported CAD version currently installed in your computer. AutoCAD 2013 is Named "AutoCAD.Application.19" and should be in your Cadversion list in CadTools settings.
If you type in ACADVER in your command line you will get ACADVER ="19.0" as answer, so you should select "AutoCAD.Application.19 in the List.
/Lars