Upgrade sql server 2000 diagram in sql server 2005 management studio

hello;

i made an application "student course registration". for this application, i used sql server 2000 as a database. i restore backup of my application in sql server 2005 studio management. the backup restore successfully. but my er-diagram is not display in database diagram'a folder. is it a upgradation problem from 2000 to 2005. there is any solution of this problem.

regards,
sumaira manzoor