Well you should follow chirpa's advice and contact tech support.
There were some updates to TiVo stuff in 4.2.15 (http://www.readynas.com/RAIDiator_x86_4_2_15_Notes
), so I thought that might help (but it appears from looking at the notes that the 4.2.15 specific fixes may not be relevant to your situation). Anyway NetGear tech support would most likely prefer you to be on the latest stable firmware, rather than on an old beta.
Updating the firmware won't solve all problems, but it's generally a good thing to try as one of the early troubleshooting steps.