Hi davobass. Internal server errors (error 500) are often caused by plugin or theme function conflicts, so if you have access to your admin panel, try deactivating all plugins. If you don’t have access to your admin panel, try manually resetting your plugins (no Dashboard access required). If that resolves the issue, reactivate each one individually until you find the cause.
If that does not resolve the issue, try switching to the default theme for your version of WordPress to rule-out a theme-specific issue. If you don’t have access to your admin panel, access your server via SFTP or FTP, or a file manager in your hosting account’s control panel, navigate to /wp-content/themes/ and rename the directory of your currently active theme. This will force the default theme to activate and hopefully rule-out a theme-specific issue.
If that does not resolve the issue, it’s possible that a .htaccess rule could be the source of the problem. To check for this, access your server via SFTP or FTP, or a file manager in your hosting account’s control panel, and rename the .htaccess file. If you can’t find a .htaccess file, make sure that you have set your SFTP or FTP client to view invisible files.
If you still have the issue you should contact your host and ask them to check the server error logs to see if they can determine the cause.
1) check .htaccess file
The first thing you should do when troubleshooting the internal server error in WordPress is check for the corrupted .htaccess file. You can do so by renaming your main .htaccess file to something like .htaccess_old. To rename the .htaccess file, you will need to login to your site using the FTP. Once you are in, the .htaccess file will be located in the same directory where you will see folders like wp-content, wp-admin, and wp-includes.
Once you have renamed the .htaccess file, try loading your site to see if this solved the problem. Before you move on with other things, make sure that you go to Settings » Permalinks and click the save button. This will generate a new .htaccess file for you with proper rewrite rules to ensure that your post pages do not return a 404.
If checking for the corrupt .htaccess file solution did not work for you, then you need to check your your php.ini file
2) Increasing the PHP Memory Limit
Sometimes this error can happen if you are exhausting your PHP memory limit.
If you are seeing the internal server error only when you try to login to your WordPress admin or uploading an image in your wp-admin, then you should increase the memory limit by following these steps:
a) Create a blank text file called php.ini
b) Paste this code in there: memory=64MB
c) Save the file
d) Upload it into your /wp-admin/ folder using FTP
