It looks OK to me:

You couldn't get NULL in Gen_DATE when it's defined as NOT NULL.

SET ANSI_NULLS ON

GO

SET QUOTED_IDENTIFIER ON

GO

IF OBJECT_ID('dbo.tblGen') IS NOT NULL

DROP TABLE dbo.tblGen;

CREATE TABLE [dbo].[tblGen](

[PROCESS_ID] [bigint] NOT NULL,

[Gen_FLAG] [bit] NOT NULL CONSTRAINT [DF_FLAG] DEFAULT ((0)),

[Gen_DATE] [datetime] NOT NULL CONSTRAINT [DF_DATE] DEFAULT (getdate())

) ON [PRIMARY]

insert into dbo.tblGen ( PROCESS_ID ) values ( 6703 ) ;

select * from dbo.tblGen;

/*

PROCESS_ID Gen_FLAG Gen_DATE

-------------------- -------- -----------------------

6703 0 2012-10-01 10:52:51.937

(1 row(s) affected)

*/