The cause of the error is actually different lines (presumably including the one just before it), because you have not qualified the Excel objects with their parent objects, it should be like this:
Code:
r = objWS.Range("a65536").End(xlUp).Row + 1 ' next empty row
objWS.Cells(r, 1) = DatePart("yyyy", Now)
objWS.Cells(r, 2) = DatePart("ww", Now)
objWS.ActiveCell.FormulaR1C1 = "=RC[-2]&""_""&""FW""&RC[-1]"
objWS.Cells(r, 3) = objWS.ActiveCell.FormulaR1C1
...in fact, you haven't even got the parent objects (objWS and objWB) set up properly, because you didn't reset them when opening a new file. You already have what you need in your code, so I'll let you work out the details.


In addition to that, instead of this line (which might close the wrong file):
Code:
objExcel.Workbooks.Close
..you should have something like this:
Code:
objWB.Close