A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
Hi,
This is happening because COUNTIF() does not work when the source workbook is closed. When you update links, the source workbook still remains closed and therefore you see the error.
Try this formula instead.
=sumproduct(1*('G:\Time Sheets\Dave Goodhand[Timesheet Period Ending 040311.xls]Week 1'!A1:U69="AD01"))
The sumproduct formula will work across closed files as well.