I also got the ERR code this morning, with a beep every 30 seconds. I bought the device on October 1, 2001, and this happened on October 16, 2008. I called the manufacturer's toll-free number and was informed that the unit has a 5 year warranty and a 7 year lifetime, and that the unit needs to be replaced. I'm guessing that this error means that its lifetime is over.
I just moved in my unit in March and my landlord was told to place Carbon Monoxide in my home and mine is doing the same Err code and I to would like to know for sure that he needs to replace with new unit and where I can get a statment to this fact.