DHCP Conflict

i`m getting IP conflicts error -but its same IP that shows up on different machine.to fix the error i did following,
ipconfig/release
ipconfig/renew
to remove it from client machine & then on server side,
i deleted the address from the dhcp database which got same ip address
also deleted mapping of same ip adress on wins
but even then it was not solving problem so i increase lease to 7 days (i`ve 50 comp iin network)
finally to get rid of error i excluded that adress from the DHCP scope.

but now a new ip address conflict came up -any permanat solution.