What do SIOCDELRT and SIOCADDRT errors mean?
Ah, silly me. After further searching, turns out SIOCADDRT and SIOCDELRT are at least related to ADDing and DELeting routes.
Because I was using a fancy subnet mask of 255.255.255.192, I didn't notice that I had the gateway set to the base address of the subnet, not the default route (In this case using .64 instead of .65).
So if anyone else gets this error, it is probably because you have the wrong gateway set. Why it errors out with "No such process" is beyond me though.