This should be fixed with 6.3.3 and higher be sure that you have the:
" fixup protocol dns maximum-length 512 "
If this does not works try:
Workarround two use the alias command:
See:http://www.cisco.com/en/US/products/hw/vpndevc/ps2030/products_tech_note09186a0080094aee.shtml
alias (inside) 10.10.10.10 99.99.99.99 255.255.255.255
!--- This command sets up DNS Doctoring. It is initiated from the clients in
!--- the "inside" network. It watches for DNS replies that contain
!--- 99.99.99.99, then replaces the 99.99.99.99 address with the 10.10.10.10
!--- address in the "DNS reply" sent to the client PC.
sincerly
Patrick