FORMERR resolving 'www.facebook.com/A/IN'
 

we have a fc6 BIND 9.4 name server which is configured as a forwader. it worked well for several months. from today morning it gives the following message for almost all domain names.

FORMERR resolving 'mail.yahoo.com/A/IN': <primary DNS server IP>#53

how to correct this? thanks in advance.