I found this rather amusing. Never encountered it before.
$ ping vg.no PING vg.no (195.88.54.16) 56(84) bytes of data. 64 bytes from www.vg.no (195.88.54.16): icmp_req=1 ttl=246 time=396 ms 64 bytes from www.vg.no (195.88.54.16): icmp_req=2 ttl=246 time=243 ms Warning: time of day goes back (-310321us), taking countermeasures. Warning: time of day goes back (-42119us), taking countermeasures. 64 bytes from www.vg.no (195.88.54.16): icmp_req=3 ttl=246 time=0.000 ms
The reason is that my laptop was shut together since the last time I pinged that address, so apparently it had cached some requests only to surface when I now tried to ping it again. It could also be due to the clock not being synchronized properly before I reached Internet again. Nonetheless an interesting error message.