Please see the notice below from the NCBFAA.
"U.S. Customs and Border Protection (CBP) has begun sending out bills for the Merchandise Processing Fee increase that was not collected beginning in October of 2011. CBP has discovered that there have been some Customs Bills incorrectly issued for additional MPF for entries that were released prior to October 1, 2011. CBP is working now to correct and stop this problem.
Our members should be alert about MPF bills issued for entries released before 10/01/11 and should instruct their clients to not pay those bills. CBP will have instructions on how those bills will be cancelled after the fix in their system is completed.As soon as CBP knows how and when these incorrect MPF bills will be cancelled, there will be a memo and/or CSMS published.”