I'm getting an error message that tells me that $admintoolsdir$ is an undefined variable. Isn't this a variable which Litestep itself defines?

make sure that $admintoolsdir$ is actually "$admintoolsdir$" (including the quotes).

Try using $CommonAdminToolsDir$

$AdminToolsDir$ will only be defined if you actually have a per-user "admin tools" directory in your start menu. To get the admin tools directory for all users try $CommonAdminToolsDir$ as DeV suggested.