I needed to disable AJAX on the profile pages in DNN due to a 4.8 bug, but I was using ajax in lots of other places, and didn't want to turn it off everywhere, so heres the fix.
(I was trying to update the BIO and add a control to upload an image)
UPDATE ModuleControls
SET SupportsPartialRendering = 0
WHERE (ControlKey = 'Edit') AND (ControlTitle = 'Edit User Accounts') AND (ControlSrc = 'Admin/Users/ManageUsers.ascx')
Be sure to restart your app after making this change.
Found on a ventrian blog: http://www.ventrian.com/Support/ProductForums/tabid/118/forumid/38/tpage/2/view/Topic/postid/27810/Default.aspx