Can't Associate .xls with Excel 2010

Hi,

I have a system that I upgraded from office 2003 to Office 2010.   It is a Server 2008 R2 system with users running remote desktop into the server.   Office 2003 worked well.

To install 2010 I used the TS Install function as always and ofcourse uninstalled 2003 first.

The problem is that no user, except the Administrator is able to open .xls files directly from the file.    The user has the option to select the program to use to open the file, navigate to the directory, select Excel, but it just does not show up on the list of program to open the file with.    Same if doing it via the Default Program in the Control Panel.    All other office docs, like docx etc open fine, even .xslx file open into Excel without
issue.   The only way to open .xls files is to open Excel first and then open the file.

I have tried, a repair, an reinstall using a different release version of Office 2010, I have even tried Office 2007, but it suffers the same issue !    Tried 32 / 64 bit version, tried various security and permission changes, tried the 2003 Office Removal tool .. tried many many things but nothing has solved the issue so far.  Microsoft say they can't help either.

I suspect it is related to the registry location of,

[HKEY_CLASSES_ROOT\Applications\EXCEL.EXE\...]  which does not exist for Excel, yet exists for all other Office applications.   But not sure on the structure and what is in the registry tree.