I've just updated Xlights to the v29 and getting these errors.
If i go back to v26 everything is fine.
I have also tried installing from the app store but i'm still having the same problem.
You may need to delete the ~/Library/Containers/org.xlights directory AND the two xlights preferences files in ~/Library/Preferences. When you start xLights, it will re-prompt for the show folder which should then setup the needed permissions. You WILL need to then go into the preferences panel and reset any preferences. In particular, you will need to set the fseq, backup, and media directories so we can once again get access to those folder.