O.K. Rockhammer; Another lesson.

Wb is the reference to the workbook which was activated at the time of
selecting Print. it is carried forward so that it can be used in your code.
Now when you have Application type events, the event will be called if you
have the workbook open and then open another workbook and decide to print
something from the other workbook. This could cause you real problems if you
do not address the situation in the code.
The following code is a demonstration to show what happens and how to handle
the situation with an if statement. You probably won't need the Else; I only
put that in for demo purposes.

Amend your code in your workbook and then create another workbook and print
from it and observe what happens and I am sure you will work out what I mean.

Private Sub app_WorkbookBeforePrint(ByVal Wb As Workbook, Cancel As Boolean)
Dim WS As Worksheet
Dim wsSel

Cancel = True 'Cancel print during testing.

MsgBox "app_WorkbookBeforePrint called from " & Wb.Name

If Wb.Name = "Test Multi Sheet Print.xls" Then

MsgBox "Correct workbook. Therefore process"

Set wsSel = ActiveWindow.SelectedSheets

For Each WS In ActiveWindow.SelectedSheets
'Note:- Next code line uses 'Now' for date and time
WS.PageSetup.CenterFooter = "&8data as of " _
& Format(Now, "yyyy-mm-dd hh:mm:ss") _
& Chr(13) & "Page &P of &N"
Next WS
wsSel.Select
Else
MsgBox "Processing skipped for workbook " & Wb.Name
End If

End Sub

Regards,

OssieMac