I am using Set mybook = Workbooks.Open(MyPath & MyFiles(Fnum)) to open
a csv file. After the file is opened I would like to make changes to
the file. The code is stored in another file Basebook. The code
works fine for opening the file and it appears that mybook is the
active book. However the changes that I make are being made to
Basebook and not mybook. The code works flawlessly in another
instance opening a different file, so it appears as though there may
be some problem with the file.

Set mybook = Workbooks.Open(MyPath & MyFiles(Fnum))
Range("F2").Formula = "=SUMPRODUCT(--($e$3:$e
$500=""Dog""),roundup(1.02*(f$3:f$500),0))"

Any ideas?
Thanks!