I am trying to build a range using the following method;

CntRef4 = xlApp.Range(xlApp.Cells(RowRef, ColRef), xlApp.Cells(z, ColRef))

Where CntRef is Range, RowRef,ColRef and z are String. RowRef,ColRef and z
all contain values when I do a mouse over, however CntRef =Nothing. If I
Change CntRef to String it reads =""

How should I look to clear upo this problem