Up until a few days ago, I was receiving all the local digital OTA channels from Milwaukee just fine. Then I went to tune in CBS and it was gone. I did a "digital scan" and it shows up on guide, I hit "SAVE", go back to guide, channel appears on guide, then hit "OK" to view channel and they disappear. I then go back to guide and they are no longer listed. CBS has 3 digital channels. Any ideas? This has never happened to me before, I'm wondering if I need to get a new 811. Thanks.