Hi, please follow these steps:
– goto HMWP Start Tab, select “Medium Privacy – More Compatibility” scheme and save the settings
– goto Permalink & URLs tab and set “rename plugins” option to “all plugins”
Note: Assuming that it’s WP single site and Apache server. Your site’s htaccess file should be writeable. Your new login URL will be http://www.yourdomain.com/wp-login.php?hide_my_wp=1234
If the contact form still gives 400 error, please try disabling “anti spam” option in HMWP general settings tab, and if still doesn’t work then try disabling IDS option in IDS Firewall tab. Let us know.
If nothing works then please let us know your website’s wp-admin login details (as private reply), so that we can have a look at the issue.