SOunds like you installed the ROM without updating to the leaked System. If so that is a known issue. You need to flash the leak in order to get the kernel needed for media playback.
GMB
Thanks for the reply bro! So even though 2.3.20 is running on Rubix, I still have to flash it again?
rubiX (Focused/Blurry) does
NOT flash you to the leak. It doesn't touch the bootloader in any way.
Upgrading to the leak is completely up to you (or, in JRummy's case, (I'm still unclear,) but I'm guessing that he just ninja convinced lots of people to upgrade to the leak without their knowledge (???).
Either way, know the risks, do the research... there is NO GOING BACK.
Edit: TBH says there IS going back. "We're working on it".
(I'm also working on building a rocket ship, and travelling to the moon. No current ETA on my trip to the moon, or their fix to let people go back to an older version of the bootloader).