Where are you opening them from? It almost sounds as if the file association for Excel files has gotten messed up on the terminal where you are opening the .xlsx file.
Internet Explorer 8
This occurs for anyone trying to open the documents (they all use Internet Explorer 8 on Windows 7 devices)
I checked the files associations, they look fine.
What happens if you save the file as a .XLS extension? The problem here maybe related to the file being MS Office 2010 inside a RH9 client publishing to RHS8. RHS8 has been out a number of years - certainly before MS Office 2010.
If i click the link, save it as a .xlsx file, then open, it opens fine...
Have you tried this on any other machine?
Did you get this fixed? I have the same issue. When testing inside RoboHelp everything is fine, the file is an xlsx and the link is connected to it. When we publish the xlsx extension gets dropped and replaced with a .zip.. the file isnt being zipped, it is simply being renamed, as is the link to it.
For starters, I'd strongly suggest each of you file a Bug Report. (link to that is in my sig)
As for the rename, I'm unsure why it would be doing that but I DO understand that the Microsoft file extensions ending in x are sort of "Zipped" versions.
Helpful and Handy Links
Try publishing to a local folder first.
I just set up a link to an xslx file and published to a local folder. The file opened in Excel as it should and the file extension was left untouched. I have never seen Rh change any file extension during publishing so if the same test works for you, I'm thinking you need to check with your IT people as to why publishing to the server is different.
See www.grainge.org for RoboHelp and Authoring tips