We can't figure anything out from the images without the rendering info and the system and AE version. It's like asking, "Why is a bananna?"
1) If you render via AE's Render Queue, do you get the right or wrong result?
2) Is your gradient layer at all transparent or using a blending mode?
Please also provide the basic info as requested by Szalam and Rick. Might help to post a screenshot of your comp's Timeline layers.
Thank you for your responses.
Here's my System Info:
Intel Core 2 Quad CPU 2.33GHz
64 bit Windows 7
ATI Radeon HD3800 Series
After Effects CS6 - Version 220.127.116.11 - all up to date
Rendering as an MP4 using Media Encoder on these settings:
Preset - Vimeo HD 720p 29.97fps
Field Order - progressive
Profile - High
VBR 2 Pass
Target bitrate AND Max bitrate both set to 5
This issue appears to be affecting just the background layer which is a solid with a ramped gradient. I've tried redering it seperately as an MP4 and using that in the main comp instead and still get the same problem.
The comp renders out mostly OK, but in the middle of the comp the background flickers to black and back again. I've rendered it out a few times previously with no problemms but this problem started appearing after I started moving the comp's camera. (this is standard 3d btw, not ray traced. RAM preview is fine. I get the same problem when rendering from within AE. These are my Processing settings:
Turn off multiprocessing for starters. 8 Gigs may sound like a lot, but not for AE. It'sw quite possible you aren't able to allocate enough memory per processor for the AE task at hand.
And you are also leaving ZERO processors for other applications.... which includes things like the operating system. Not good.
Thanks for posting all the extra detail. Can you also post a screengrab of your timeline with any relevant parameters (like opacity and transfer/blend modes) visible?