How to permit ALL on my PIX501 fw?
You need to open the ACL, only if there is one on the inside high security interface.
If you are pinging from an inside host you will not be able to ping the outside interafec of the ASA, only the inside.
For being able to ping outside hosts check your natting on the firewall. You need to translate the inside host in such a way that the outside host has a route back.
I hope it helps.