Failed to change the screen configuration!

schkiki

1920x1080 -> 1024x768 (Fail)
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firefly@firefly:/$ xrandr --props
xrandr: Failed to get size of gamma for output default
Screen 0: minimun 1920 x 1080 ,current 1920 x 1080, maximum 1920 x1080
default connected 1920x1080+0+0 0mm x 0mm
     1920x1080            0.0*

firefly@firefly:/$ xrandr --newmode 1024x768 65.00 1024 1048 1184 1344 768 771 777 806 -HSync -VSync
xrandr: Failed to get size of gamma for output default
firefly@firefly:/$ xrandr --addmode default 1024x768
xrandr: Failed to get size of gamma for output default
firefly@firefly:/$ xrandr --output default --mode 1024x768
xrandr: Failed to get size of gamma for output default
xrandr: Configure crtc 0 failed
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Unable to read from the edid data.
Please show me how.