What version of SQL Server are you trying to deploy to? First, try to deploy a new instance of your database to a SQL Server 2005 instance (Express is fine). This will just prove that the package is fine. If you are deploying to SQL Server 2000 then you will want to be sure and download either the latest 1.6.5 build or the 1.6.6 beta as there was an issue in regards to the extended properties at one point a while back.When the DDT deploys, it flags the database, UDFs, views, and sprocs with an extended property that indicates that the component was deployed using the DDT, so if a DBA or some other IT person adds their own views, UDFs, sprocs, etc. it will not remove them when updating. That is what is giving you the error it would seem.
So version details, etc. will be helpful. Thanks.