Hi Gloria,
I definitely didn't expect such a prompt response! Kudos to you and Microsoft!
Good news: I found the error and fixed it.
I think what's happening is sometimes, if Excel desktop app crashes with an online document being open, a conflict is created between a newer version of that online file (maybe because someone else modified it online) and the file that Excel cached and has in queue to upload. So I went into Microsoft Office Upload Center and canceled/deleted any files in queue for upload or save.
That seemed to have taken care of the issue, and I could open in Excel desktop the file that lives in the Sharepoint site. :)
Regardless, I almost had an aneurysm when this happened (two times). It would be good to either prevent that from happening through a patch or fix, or letting your community know how to handle this type of situations - especially because in this case Excel desktop app just crashes and shuts down without any error message whatsoever.
Thanks for the fast response!