the error.txt is empty.  Is the Excel out of date or the Netezza datasource?

I see the error now.  By default, when publishing workbooks that connect to desktop files (i.e. Excel), Tableau Server will "include external files" which under the covers means that it will point at the temp copy and then when you try and refresh, you get this error.  How we have dealt with this is:

1. Within your workbook, attach to the Excel file via UNC path.  (i.e. \\servername\sharename\abc.xlsx)

2. Make sure the runas server account has access to this sharename

3. Uncheck "include external files" when publishing

It looks like the Excel files are:

1. in a temporary folder, which is never good. 
2. being saved on the Tableau Server itself which isn't a good idea, either.