Problem deleting expired leased IP addresses

Hi All

we are having problem with our DHCP server. for a scope the lease time is 1
hour and the IP's doesnt get freed after 1 hour in the scope. this ends up
using all the available IP's in subnet although actual used IP's maybe half.
the IP's whose lease expiration time is expired have white icon with a blue
exclamation mark in the scope list.

the server is a windows 2003 server with all the latest patches installed.

has anyone faced similar issues???

your help highly appreciated.

Thanks & Regards
Aasim