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!