I recently attempted to upgrade to Omeka S 4.0, but receiving an Internal Server Error. The server settings are the same as when the previous version of Omeka was working. All of the modules (except for EasyAdmin and Log) have been removed to make sure there isn’t a conflict with the new version of Omeka S and the error message remains. The .htaccess file and application.log file updated to display and errors and the application.log file is empty. I am truly at a loss on what could be causing the error. Is there a way to fix this other than reverting back to the previous version of Omeka and giving he upgrade a try at a later date?
Sometimes folder permissions get messed up in the upload process from the zip files. Have you checked to make sure that the directories are set to 755 (aside from the files folder) and the files are set to 644?
This is just a guess, but it happens to me when I update from the zipped release on my Reclaim Hosting instance.