Not sure why you are first selecting the nodes with VOLT value? You have not applied it yet. I think the "nsel,s,d,volt" is returning zero nodes and so when you do "nsel,r,loc,z,0" you are getting nothing. I would remove the "nsel,s,d,volt" command and just do "nsel,s,loc,z,0"
Also you can do a DLIST to make sure the voltage bc is applied.