I believe my current install of Excel is corrupted. Every time I try to open a file, I get the Error: "This file is corrupt and cannot be opened." However, I can immediately try again and it opens just fine. Clearly the file is not corrupt, and it opens fine on all my other computers.
I don't have a solution but make sure when it re-opens then "send a frown" via the smiley faces in top corner or via File > Feedback. The Excel team will then get a log and it will help them identify any common bugs