what kind notice could it be? 149482006-01-05 01:40:54

I got a email message from CIS as follows. I will call them later. My question now is what kind notice it could be? Thanks.
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Current Status:

Our last written notice in this case was returned as undeliverable by the post office on November 7, 2005. To update the mailing address so this notice can be re-sent, please call the National Customer Service Center at (800) 375-5283.

and it is a I-485 case

回复：and it is a I-485 case

The same message in the on-line status