options registration page section doesn't show drop down

In the options > membership page > registration page there are no drop down list of the page
I could use.

When I use create page, it does create a page, but when I click on view page it display a blank page.

I would like to use a page already created so I can set the good slug which can't be modify with the auto generated page.

Can't find this in the manual and in the video?
running WPMU dev v3.5.2
clear the cache multiple time
tried the shortcode
I am disapointed because I bought this 1hour ago and I ran into the first bug after 20 min of use............