When you migrate from Server 2003 with export, you will see a Red X in address leases section.
You should do the migration as follows:
Open command prompt in Server 2003 and type:
netsh dhcp server export C:dhcp.txt all
Open Dhcp console in the new Server.
Open Administrative command prompt on the new Server and type:
netsh dhcp server import C:dhcp.txt all
Right-click server name in Dhcp console and choose refresh:
Then you will see the leases again.
Have a Great day!