Hi all,
We've found the solution to this problem.....
The IT Department used a tool to watch what happens while installing...
and that discovered that a key is missing in the registry....it is the following one:
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Office\14.0\Excel\InstallRoot
I suppose that this might help others with the same/equal problem.
have a nice day!
Season greetings
Greg