I am able to add Galleries to Posts just fine using the Upload/Insert Add an Image feature.
I have a problem once the Gallery has been added to the post - and looks like a Large Blue Box with picture icon - and the Delete and Edit buttons on the top left.
Clicking the Edit Button on a Gallery that already exists in a post gives me the error below in the overlay window that should be showing the Gallery Edit Screen.
-- notice the double slashes after wp-admin --
The precondition on the request for the URL /wp/wp-admin//media-upload.php evaluated to false.
Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.