unhandled error 4004 silverlight major issue child element

Can get the dread element already has a child element error...this is very generic.
Get the right error
Run f5, go debug , windows, processes and select all processes and right click with mouse to detach.
Run the program until get an error eg. data form scrolling and it blows up

Should get a better error message e.g load operation failed for query 'GetUser'

This error in the dataform scrollling up and down and it blows up after while caused by messing up web.config...some forms authentication stuff left in

esp fix up to have profile enabled =false and rolemanager enable and set up
set up identity impersonate=true