Hi,
1: From which side you are initiating the PING? Is the behaviour same if you initiate the PING from either side?
2: What do you see in ">show security ipsec statistics"? any error?
3: any screen drop in the interface/zone etc
show security screen statistics ?
Possible completions:
interface IDS statistics interface
ip IDS statistics ip
zone IDS statistics zone
Thanks,
Vikas