I've got 2 site running WordPress 3.9, SEO Ultimate and Gravity Forms
Both sites run the same framework.
Both site run SEO Ultimate Version 184.108.40.206
One site is running GF 1.8.6
One site is running GF 1.8.7
The site with GF 1.8.6 works fine.
The one with GF 1.8.7 when you go to click on the Add Form button when editing a post of a page there's a popup where you can select which form to insert and then hit the button to insert the shortcode in to the page or post. However, when the popup shows up, it shows up behind the overlay. So when you go to click on anything the popup closes.
When I checked the CSS there's an ID called #TB_overlay that comes from thickbox. The z-index set in the stylesheet for that ID is 100050.
When I checked the popup for the Gravity Forms window the ID for that is #TB_window which has a z-index of 100002 (which puts it behind the overlay) and that z-index is being set by sdf.admin.css from SEO Ultimate.
Upping the z-index in your stylesheet fixes the issue.
Just thought to pass on the info.