If it only happens when you close one workbook, maybe using Bill Manville's
FindLink addin would help you find the problem link.
You can find it here:
> Suddenly I am getting the following message when I try to close a workbook:
> "Your formula contains an invalid external reference to a worksheet.
> Verify that the path, workbook, and range name or cell reference are
> correct, and try again"
> The mysterious thing is that it does not happen consistently and that, after
> I click OK after the above message, I can still save the file.
> What might be the cause of this error message and can the "invalid
> reference" be tracked down using one of the utility add-ins such as J.
> Walkenbach's PUP?