Could you tell me the meaning of 'Should have obtained video_window_handle by now!' ?

[Fred]

 I am building GTK+ & Gstreamer with 4 network IP cameras. But I have a
problem with
' gst_element_set_state (source_data.pipeline[0] , GST_STATE_PLAYING)'
function.
I declared pipeline[4] because I will use 4 cameras. But
gst_element_set_state() function only display the last video window.
Currently 4 videos  display on not 4 drawing areas but one drawing area.
I don't know how to display on 4 drawing areas with 4 cameras.
cf. env : ubuntu, gtk+3.0, gstreamer 1.8.3

Thank you for any reply in advance.
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