Recently one of our customers asked to make the popup forms for send to friend and send enquiry only available to logged in users, we wrote a small snippet of code for it and though we would share it. (this code would be placed in you child theme functions.php file)
Now when trying to open one of the send to friend or send enquiry forms you are shown a message and given an option to login/register, if the link is clicked you will be taken to the login page and then redirected back to the original page.
(From GeoDirectory 1.6.3+ when redirected back the popup form will automatically open up)
The GeoDirectory Team