"The database schema is too old to perform this operation in this sharepoint cluster. Please upgrade the database and try again".
This message appears when trying to perform a restore with SharePoint Portal Server 2003 - and there are version differences between the machine where the backup is from, and the machine where you want to restore it on.
Make sure you have installed all the security updates
, service packs
on the system
, SQL Server/MSDE
on both machines. After that, create another backup and try to restore it.