Web Viewer doesn't allow to Export reports to Excel. Need confirmation that option Export is not installed.
The error message is:
This XML file does not appear to have any style information associated with it. The document tree is shown below.
On another PC could open the XML document with EXCEL. So its not a problem with the XML file. It's a problem with your XML handler on that PC.
As a circumvention, start Excel, and open the XML document.