WooCommerce Currency Switcher

• https://wordpress.org/support/topic/general-settings-403-error-when-saving
• http://stackoverflow.com/questions/12928360/how-can-i-disable-mod-security-in-htaccess-file

It is something related to the mod_security rule on your server. Made necessary changes with the mod_security and it may help to resolve the issue.

Please ask for it in your hosting support ...