The address you are trying to monitor should be reachable using the interface the gateway is attached to, either directly or using a static route (check System › Routes › Status).
dpinger:.. sendto error: XXX
Usually found in System › Log Files › General, every code has a meaning, usually explained in errno.h (man errno)
Some common ones are explained in the errno section.
arpresolve: can’t allocate llinfo for..
This message usually means that the configured gateway lies outside the configured subnets for this firewall (for IPv4).