I used AE CS6 Version 126.96.36.1998.
I rendered in mp4 codec H.264 1280x720.
I using Win 7 Home Premiere, Fujitsu Lifebook AH531.
I used C4D to redered out my PNG sequence and then import to AE,
then I added RSMBlur by RE:Vision Effect then I used RAM preview on AE, it was ok.
But when I rendered in mp4 format, the video became like this.
I tried to render as JPEG sequence, mov format also don't work, the result look weird like the image I posted above.
I'd highly recommend updating your After Effects. You are missing some major bug fixes. The latest version of CS6 is 11.0.4.