|As already mentioned, there must be another DHCP server on your network - probably your router. Your clients are getting an address and the DNS server address from there. This means they won't be using your server for DNS, which explains the error message.|
Also, on a simple network, you should use the same network for your clients as for your server. You need to turn off the rogue DHCP server and reconfigure the range of addresses given out by your server so that they are on the 192.168.0.0 network.
This is assuming an isolated network and that you are not part of a larger network (e.g a college network).