hello learoyd,
this is an informatinal (critical) message. you need not worry much about it...
just have a look at the below explanation.
Error Message %PIX-2-106013: Dropping echo request from IP_address to PAT address
IP_address
Explanation This message is logged when the firewall discards an inbound ICMP Echo Request packet with a destination address that corresponds to a PAT global address. It is discarded because the inbound packet cannot specify which PAT host should receive the packet.
Recommended Action None required.
All the best. rate replies if found useful !!!!