The website encountered an unexpected error. Please try again later.

The website encountered an unexpected error. Please try again later.

This is a generic message. To find the problem refer to server log. (For example : /var/log/apache/error.log on apache)

Case 1 : File access permissions

[pid XXXX] (XX) Permission denied: [client IP] XXXX: /home/drupal/public_html/drupal8/.htaccess pcfg_openfile: unable to check htaccess file, ensure it is readable and that '/home/drupal/public_html/drupal8/sites/' is executable, referer: https://domain/admin/config

.

[core:crit] [pid XXXX] (XX) Permission denied: [client IP] XXXX: /home/drupal/public_html/drupal8/sites/default/.htaccess pcfg_openfile: unable to check htaccess file, ensure it is readable and that '/home/drupal/public_html/drupal8/sites/default/' is executable,

If you see an error like this probably your site has a problem. Please check files/folder access permissions.

• drupal/sites/
• drupal/sites/default/
• The Temporary files directory (default /tmp (/admin/config/media/file-system))
• Private files directory

To test enable file access using following command from drupal root : chmod 0755 . -R

Plugin Not Found Exception at the drupal install

I got his error at the installation of drupal from Development to Production environment. I haven't fount any different, but problem resolved after re copping all files from local to production.

Id you use git on Production server, check if there are unwanted .git files (or .gitignore) on your modules. If there any, remove and re try.

[fcgid:warn] [pid XXXX] [client IP] mod_fcgid: stderr: Uncaught PHP Exception Drupal\\Component\\Plugin\\Exception\\PluginNotFoundException: "The "tag" plugin does not exist." at /home/drupal/public_html/drupal8/core/lib/Drupal/Component/Plugin/Discovery/DiscoveryTrait.php line 52