Cannot save sql server database diagram

 For example the database is adventureworks and you want to save the diagram there.

Connect to adventureworks db and then issue this command.

DROP TABLE dbo.sysdiagrams;
GO
CREATE TABLE [dbo].[sysdiagrams]
(
    [name] [sysname] NOT NULL,
    [principal_id] [int] NOT NULL,
    [diagram_id] [int] IDENTITY(1,1) PRIMARY KEY,
    [version] [int] NULL,
    [definition] [varbinary](max) NULL,
    CONSTRAINT [UK_principal_name] UNIQUE ([principal_id],[name])
);

GO
EXEC sys.sp_addextendedproperty 
  @name=N'microsoft_database_tools_support', 
  @value=1 , 
  @level0type=N'SCHEMA',
  @level0name=N'dbo', 
  @level1type=N'TABLE',
  @level1name=N'sysdiagrams';
GO

Then save it again