Sony k750 facia changed camera now not working,why?

Having changed the facia on my k750i the camera does not now work . when camera is selected the message appears saying open lens cover,which when done does not make any difference...I have only changed the front and back covers and not tampered with the internals on the phone.. any ideas please......

perhaps the new cover is not fitting 100%... try the old cover back on and see if its ok,, then you know.......

Its probably not on properly