Just encountered this problem running Dude on Win XP SP3. The UAC tip was a good one - put me on the trail of a permissions problem.
Dude was working fine... I rebooted for an unrelated issue. Upon starting Dude again ALL my ping probes failed, giving a reason of a local problem. All other probes were fine.
It turned out that my domain logon privileges had been reduced and I picked up the reduction after the reboot. Increasing my privileges up to local PC admin rights fixed the problem and all my ping probes started working again.
I hope this helps,