win2000 will not release ip in shut dwon

Our dhcp is on win nt server. The problem we are having is when windows 2000 shuts down it will not release the ip address if I run a batce file with ipcongif/release under the shutdown script on MMc then win2000 will release the ip address fine. Weset our dhcp lease to 5m. Dose any one have thae same problem .