MS SQL SERVER 2005 BUG? Cannot insert NULL into column diagram_id

Hi friends,
when trying to save a diagram I got an error:
The sp_creatediagram procedure attempted to return a status of NULL, which is not allowed.
Whats with this??I had the same issue an just fixed it by turning the "diagram_id" field in SysDiagrams table to "identitity".

I dropped the table and ran the following script.

CREATE TABLE [dbo].[sysdiagrams](
[name] [nvarchar](128) COLLATE SQL_Latin1_General_CP1_CI_AS NOT NULL,
[principal_id] [int] NOT NULL,
[diagram_id] [int] identity(1,1),
[version] [int] NULL,
[definition] [varbinary](max) NULL
) ON [PRIMARY]

It worked.