What is the exact version of Excel Office 365? Ideally i'd try to install that exact version and see if I can reproduce. We're using a Microsoft Library to launch a Microsoft Product - I don't know why it's failing to load of all a sudden, but I'd guess an update to Excel or your operating system.

Also, can you 

• Open ProSeries
• Go to Help -> Send Logs
• Email the resulting zip (saved to your desktop) to proseries_engineering@intuit.com