You need to allow ICMP Echo Requests outgoing and both ICMP Echo Replies and ICMP TTL Expired returning packets. We don't have this router anywhere inhouse, so I can't offer you much advice on how to configure it.

The good news is that most ICMP is relatively safe (some bugs in routers have allows ICMP to be exploited, but most of those bugs are no longer outstanding). A lot of routers block ICMP more for reasons of discovery rather than safety.