It's been quite a while since I had this problem, but it's very likely that the "troublesome" IP address was in fact 192.168.0.199. I doubt that there's anything special about this IP address, other than the fact that it's the first one automatically assigned by the router, if the router is setup with the default DHCP IP Address Range of 192.168.0.100 to 192.168.0.199 (If I remember correctly, earlier hardware versions of the DIR-655 started at the other end of the range, i.e., assigned 192.168.0.100 first).
In my case I have a number of devices (e.g., printers, camaras, NAS devices, etc.) hardwired to my router and have reserved IP addresses for them at the top of the list. I normally connect my laptop via wi-fi, so I've reserved an IP address for it farther down the list (e.g., 192.168.0.188). So when I was changing the firmware version of the router, it's configuration would have been wiped, and with the laptop hardwired to the router (wi-fi not setup at this point), the router would have assigned it the first one in the range (i.e., 192.168.0.199). Thus the reported conflict when the configuration file was loaded (which would have contained 192.168.0.188 as the IP address for the laptop).
As I said earlier, I'm amazed that the router actually checks.