If you are having an issue where a pop-up like above is showing up when using Microsoft applications (Excel, Powerpoint, Word), this can be fixed by following the steps outlined below:
1. Quit out of all Microsoft applications.
2. Open Finder > Applications
3. Select Microsoft Word and get to the Get Info dialogue box by pressing Command+I or by pressing Command while clicking on Microsoft Word and selecting "Get Info"
4. Enable the "Open using Rosetta" checkbox and close the Get Info pop-up.
5. Repeat Steps 2 and 3 for Excel and Powerpoint.
6. Restart the computer to ensure that the changes take place.
Note: It might take a little while for the applications to open for the first time after making this change.