I had the same message when I tried to start my car yesterday morning. I found this topic and forum from a google search.
If you have a backup key...try that first. My issue was the key. I must have dropped or done something to it. Unfortunately the dealer needs the car in order to program the key. That required my V70 be towed to the dealer and they took care of the rest. I had already purchased a new key but had not had it programmed yet. The programming cost $140 but I ended up paying a small diagnostic fee since it was not certain what the problem was.
Lesson learned...have an extra key and have it programmed. In this instance I would have saved about $150 in just the towing and diagnostic fees...
2001 V70 2.4T