2011 mac edition. Cannot access the file in "macintosh hd"

[handhglassworks]

Good morning. We are unable to save updated versions of our documents on 2011 Excel for Mac. We've clicked (so we think) the boxes that give permissions, yet it never works. We continue to the an error box that says, "Microsoft Excel cannot access the file 'Macintosh HD.'" I will attach a screenshot. Please help. We're idiots and could really use it.

Thanks in advance.

Greg

[handhglassworks]

Any takers? I am not even able to "Save As" in order to rename it.