Help Pls - 485 Current Status: Notice returned as undeliverable,

485 online status shows: On November 8, 2007, the post office returned our last written notice on this case as undeliverable. This can have serious effects on the processing of this case....
Called the number, told them I have never changed and received my EAD and FP notice last month. The lady told me she would send a message to the officer to requst resend, but she cannot tell me the address in the system, nor the content of the notice.
Has anyone experienced the similar situation and can advise? Thanks in advance!