DHCP giving out bad IP Addresses

We are running DHCP Server at work. My end users login by my BDC. Recently I have noticed that My DHCP is assigning Bad IP Addresses. Causing Conflicts. I have checked my DHCP Manger and I have checked all end users to make sure there is no conflict with a static IP Address. Do you have any thoughts on what could be causing this? It seems to only happen to the workstations running Windows 95 not NT Workstation.