Subtotal another open sheet in VBA

I am trying to use the worksheet function along with Subtotal to get the
total of a range on another sheet and place it in the main spreadsheet.

Cells(49, C) = Workbooks(WrkBk).Worksheets("Billable
FT").WorksheetFunction.Subtotal(9, xlRng)

Where XlRng is Range, WrkBk is a value from an array. If I remove the
worksheet and workbook references, it runs locally.