This happens rarely and can be solved by clearing cached content from Internet Explorer browser.
Please follow the steps given below to fix the issue:
- Close the Add-in
- Open Internet Explorer on your PC
- Clear browsing history and temporary internet files by following the instructions given here.
Note : Microsoft Add-Ins rely on Internet Explorer, not your default browser, for certain functions . It is important that you clear cache on Internet Explorer, not your default browser.
Also see :