Hi mr.me, if setting permission to 644 for the htaccess file does not help then please follow these steps:
1) make a copy of your original htaccess file
2) goto HMWP >> ‘Start’ Tab >> ‘Medium Pripacy – More Compatibility’ scheme >> click ‘Save Settings’
3) open htaccess file and copy HMWP plugin’s rules (lines between RewriteRule ^index\.php$ – [L] and RewriteCond %{REQUEST_FILENAME} !-f)
4) Now in your original htaccess file add the lines you copied in step 3 (betwwen the same lines where it is copied from)
5) make htaccess file read-only
Note: Assuming that it’s WP single site and Apache server.
If you are still having issue then please let us know your website’s backend details and FTP details so that we can fix it for you.