IP conflict (server 2003) Firewall box

In our network we have 20 servers on the LAN that are using the following static IP address e.g. 607.67.78.1 and 200 work station that are on a DHCP using the following range 607.67.68.1. The problem is my firewall server got an IP conflict we traced and found that it was conflicting with one of the workstation using the following range 607.67.68.1. how is this possible how can I stop it please help