Partha,
Try one of these two methods.
1-
access-list 101 permit icmp any any echo-reply
access-list 101 permit icmp any any source-quench
access-list 101 permit icmp any any unreachable
access-list 101 permit icmp any any time-exceeded
access-group 101 in interface outside
or
2-
policy-map global_policy
class inspection_default
inspect icmp
Check this link for more details on PIX/ASA ICMP and traceroutes handling.
http://www.cisco.com/en/US/products/hw/vpndevc/ps2030/products_tech_note09186a0080094e8a.shtml#topic0
Rgds
Jorge
Jorge Rodriguez