You really shouldn't have to do anything.

That being said I have a client right now that uses Citrix Xenapp and they can't get explorer to work.   Works for me with administrator rights.  So my assumption is they don't have proper security rights in some folder, but I don't know which folder yet.

when or if you ever find out, please let me know!

This has happened to me in the past and the answer is that it is looking in the wrong place to open Excel. On some computers you might have more that one Microsoft Office folder.  Can't remember right off the top of my head where to edit, probably in the Knowledge Base. But you have to direct it to the correct Excel location.