From what direction are you trying to ping the outside interface? If you are trying to ping the outside interface of the pix from a network on the inside of the pix, not gonna happen. If your on the outside of the pix, you should by default (if your on the same subnet, otherwise you need configured routes etc) be able to ping the outside interface. You might look at your configuration to see if there is a command that says "icmp deny any outside". If its there, change it to permit, which was the default. Good luck.
Kurtis
