Many people in the TivoCommunity.com forums who have hacked their TiVos to add additional hard disk space are finding that the latest firmware upgrade, 3.1.0c (which started hitting boxes about two weeks ago), is causing intermittent picture freezing and lock ups. These aren't people who have done anything crazy to their boxes necessarily, either; Many of them simply replaced dead, stock hard drives with new units. If you've had a similar problem, I'd head over there and try to work it out together. A group of concerned users working with TiVo will do a lot more to fix the problem than sending an email to me would (hint hint).
Read - 3.1.0c Warning

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