192.168.18.77 - 192.168.18.2 - SPI:0x90404248
The second address is the domain controller and DNS & DHCP server. Why would either of these be an illegal host? (Which one is Sonicwall complaining about, BTW? Some types of alerts put the violating address first, and other alerts put it second.)
This is the only such occurence, and no network configuration has changed in over a week.