Off the help file:Variables
If you specify a %variable name in a dialog item definition, the %variable will be set with the contents of that item when the dialog is closed.
edit "", 2, 10 10 100 20, autohs %result
Maybe this is what's wrong. mirc thinks that %nlistpath is there for the above purpose. Try
or, if that doesn't work either, make a custom identifier like
alias nlistpath return $+(",%nlistpath,icons\op.ico")
and put $nlistpath in the icon item.