Visual Baisc 2005 Express Edition and SQL 2005 Database Diagram Tools

Hi,

I have created a database using VB Express 2005 express edition and I have created number of tables and SP's etc.

I am trying to use the database diagram tool but I get an error stating that the database doesn't have a valid dbo. I say yes to the prompt about making myself a valid dbo but I then get a message stating that I do not have permissions to imprersonate the dbo.

How do I overocome this issue?

Thanks

Bill