Address confilcts with DHCP

We’re running a 98SE over NT network using DHCP on the file server. About once every 6 months, we have a rash of address conflicts: server trying to assign same address to two users. Our scope is plenty large so that people shouldn’t be stepping on each other. I can fix it by deleting the address in DHCP manager, and releasing and renewing from both client machines…but it’s a pain and it shouldn’t be happening. Any ideas?