Enable Legacy Mode
Legacy mode is a replacement to the "Enable Proxy Field Method" checkboxes of earlier editions of Hide My IP. As the help file describes, it uses an older method to hide your IP.
Checking that box means that version of the software will not support many features such as encryption or hiding your IP in non-browser programs.
Hide My IP is designed to detect when this option is needed. The only reason you should tick this box is if you are advised by support or if you are a very advanced user.
Checking this box will cause Hide My IP to use a different method of hiding your IP address. When Legacy Mode in enabled, your IP will not be hidden with any browsers in the "Enable Other Known Browsers" setting nor any programs in the Premium list of Additional Supported Programs. The "Encrypt My Connection" setting will also not be available.