Having a quirky issue

I've set up a macro that runs fine on my system but isn't working on a
co-worker's system (and it had been working fine for a couple of months prior
to now). Here's the code:

Range("B11").Select
ActiveCell.FormulaR1C1 =
"=IF(LEFT(RC[-1],1)<""A"",IF(LEN(RC[-1])=14,LEFT(RC[-1],5),Left(RC[-1],4)),VLOOKUP(RC[-1],'[FA Vehicles PCard DO NOT DELETE.xls]Sheet 1'!C1:C2,2,FALSE))"
Range("b11").AutoFill Destination:=Range("b11:B" & endRow)
Range("b11").Select
Range(Selection, Selection.End(xlDown)).Select
Selection.Copy
Range("b11:b" & endRow).Select
Selection.PasteSpecial Paste:=xlPasteValues, Operation:=xlNone,
SkipBlanks _
:=False, Transpose:=False

Basically, it copies the formula down the column. On her system, the
formula works in the first cell but then copies the result from the first
cell down -- not the formula, so the whole column has the same data.

We're using the same source data. I've tried reinstalling the macro on her
system but it's still not working. We have the same versions of Excel (2003)
and VB (6.5). The only thing that is different recently is that she's
learning macros and has been playing with the system (but hasn't touched this
macro -- even if she had, I've reinstalled it so this shouldn't be an issue).
I've tried deleting her personal workbook and reactivating it, but no luck.
Any ideas?