Private Page Pop Up Solution

Can anyone please recommend a lightbox pop up solution that will restrict access to a page until a visitor enters in name, email, phone number etc..

What I am hoping for is:

If visitor tries to access particular page – pop up requesting info to view page.

Once entered the page is displayed. No “login” or “registratoin” required per se.

If they do not enter in the info, an error message. And they cannot close the pop up box.

I would like to be able to use this with Gravity Forms.

Can someone please help??