What kind of "range" does WorksheetFunction.Max need?

Starnge problem here (maybe my dumb error...)

This works:

msgbox WorksheetFunction.Max(Worksheets("data").Range("A6:A10))

This doesn't:

msgbox WorksheetFunction.Max(Worksheets("data").Range(Cells(startrow, B1var(i)), Cells(endrow, B1var(i))))

I need variable columns and rows, that's why I need the 2nd style. At the beginning I Dim B1var() As Variant and then again ReDim B1var(1 To numbldsec) where numbldsec is an integer, but not sure that matters. startrow and endrow are not declared, but check out as integers.....

Any ideas?