Sounds like it doesn't like 192.168.200.31 and above. Is the subnet mask set correctly? If it were 255.255.255.224 (i.e. "/27"), then the behaviour you report would be correct. Or is the router itself on 192.168.200.31? Don't forget to allow for its own IP address in your calculations.

I just tried on my WRT54G and it's fine with starting at 192.168.1.100 and max 155 users (netmask is 255.255.255.0 or "/24").

Peter