We have a Safari extension that's been up on the App Store for about 18 months with no apparent issues. This week, however, while working on an update, we uninstalled the production version on our test machines and installed a developer version. When we had some issues, we tried to go back to the production version downloaded from the App Store, but we get an pop saying "Unable to download App." In the log, the most obviously relevant error is 'Operation not permitted'.
This occurs on several machines and different logins on those machines in both norma and safe modes. However, on another machine that never had one installed, we could still install the app from the app store, so I suspect there is something left behind that needs to be removed, but I don't know what.
FWIW, I see the download directory getting created under /Applications, but it is promptly removed when the failure popup appears.
Any suggestions?