Listbox issue

I am trying to populate a listbox with cells Z1:Z2 and for some reason when I enter that into the listfillrange in the properties for the listbox and hit enter the listfillrange goes blank and nothing displays. If I name the range it will populate however I don't want to do that. Also this worked fine in the past I am just now converting the spreadsheet from excel 2003 to excel 2007 and when I opened it on 07 I found that this functionality was lost.