Did you update your Apple TV to iOS 4.2 (yeah, it says 4.1 sometimes, 4.2 others, let's consider it both) this week only to find you still had HDCP (high definition copy protection) problems, or worse, only to find you now had HDCP problems, maybe with Netflix in specific? Georgia's experiencing that today, and so are some members of our Apple TV Forum. Well, we'll try to help you out after the break
First a rant by way of explanation: HDCP is a horrible plague visited on paying customers by movie and television studios that consider us all criminals out to steal their content. They think it stops piracy but -- irony of ironies -- real pirates know how to get around all types of copy protection and it's usually only real customers who suffer from schemes like HDCP. Basically it enforces a secure HDMI connection from content box (Apple TV, Blu-Ray player, etc.) through intermediaries (like a receiver) to output (TV). Every link along the chain has to be secured with HDCP in order for your video to play.
This is why your Apple TV (or other video equipment) might occasionally barf up a "not HDCP compliant" warning and refuse to play the Netflix you subscribe to, the content you rented or bought from iTunes, or other DRM (digital rights management) inflicted video.
Here's what you can try to do to work around it in general, in order of severity and annoyance.
You'll still have the nuclear option of taking your Apple TV to an Apple Store and maybe even swapping it out for a non-inflicted unit but start with the above and let us know if it works for you. If you have any other trouble shooting tips, let us know about those as well, and make sure you check out our Apple TV Forum for more expert help and advice.