Pages used for selecting objects have to be based on a pop-up layout. Check the 'Layout type' property of the layout of the 'Account_Edit' page. It should be 'Modal pop-up' or 'Pop-up'. Perhaps it is 'Legacy' in which case the thing that opens the page (here the button) determines how the page is opened. The best solution is to move away from 'Legacy' layouts.
For more information see the article Layouts have types.
Ok thanks solved!