I got the same REF email.
Looks like computer glitch.
DO: Baltimore, MD
07/27/09: N-400 for self and wife mailed to Texas by certified first class mail.
07/30/09: N-400 Received
07/30/09: Priority Date
07/31/09: Checks cashed
08/06/09: NOA received
08/06/09: FP Notice Date
08/11/09: FP Notice (self and wife) received
XX/XX/XX: FP done
XX/XX/XX: IL Notice Date
XX/XX/XX: Interview Letter received
XX/XX/XX: SSL letter received
XX/XX/XX: Interview Date
Looks like computer glitch.
DO: Baltimore, MD
07/27/09: N-400 for self and wife mailed to Texas by certified first class mail.
07/30/09: N-400 Received
07/30/09: Priority Date
07/31/09: Checks cashed
08/06/09: NOA received
08/06/09: FP Notice Date
08/11/09: FP Notice (self and wife) received
XX/XX/XX: FP done
XX/XX/XX: IL Notice Date
XX/XX/XX: Interview Letter received
XX/XX/XX: SSL letter received
XX/XX/XX: Interview Date