W3 Total Cache Plugin writing to htaccess file
As Denis stated the W3TC-plugin indeed writes to your .htaccess-file. This way the different functions are enabled through apache in the visitor's browser ...
There are some bugs on the W3TC-forum on the plugin writing corupt .htaccess & nginx.conf -files, but try:
- Updating the plugin to the latest version
- To enable one function at a time to see which function causes the 500-error
Deleting the .htaccess file effectively prevents W3 Total Cache operation. You need it if you are going to run W3TC.
This 500 error has happened to me and my clients on a few occasions. I would suggest that you:
Empty all caches via the WP admin area "Clear all caches" button.
Allow W3TC to write to your htaccess file by modifying any setting(you can change it back afterwards).
Clear your browser's cache and cookies.
Works for me.