Entity Framework 6.4 cannot delete Relationship Record

Question

I have 3 tables Groups, Organizations and Rel_Group_Organization

I am trying to delete a record or all records

BO.RelGroupOrganization.Clear();
BO.RelGroupOrganization.Remove(record to delete);
_context.SaveChanges();

when saveChanged I get the following System.InvalidOperationException: 'The operation failed: The relationship could not be changed because one or more of the foreign-key properties is non-nullable. When a change is made to a relationship, the related foreign-key property is set to a null value. If the foreign-key does not support null values, a new relationship must be defined, the foreign-key property must be assigned another non-null value, or the unrelated object must be deleted.'

Here is my configuration

public RelGroupOrganizationMap()
        {
            ToTable("REL_GROUP_ORGANIZATION");
            Property(e => e.Id).HasColumnName("ID");
            Property(e => e.GroupId).HasColumnName("GROUP_ID");
            Property(e => e.OrganizationId).HasColumnName("ORGANIZATION_ID") ;

            HasRequired(s => s.Organization).WithMany().HasForeignKey(key => key.OrganizationId);
            HasRequired(s => s.RapidGroup).WithMany().HasForeignKey(key => key.GroupId);
        }

here is my class

public partial class RelGroupOrganization
    {
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int Id { get; set; }
        public int GroupId { get; set; }
        public int OrganizationId { get; set; }
        public virtual LuOrganization Organization { get; set; }
        public virtual RapidGroup RapidGroup { get; set; }
    }

finally here is the sql for the table

CREATE TABLE [dbo].[REL_GROUP_ORGANIZATION](
    [ID] [int] NOT NULL,
    [GROUP_ID] [int] NOT NULL,
    [ORGANIZATION_ID] [int] NOT NULL,
 CONSTRAINT [PK_GROUP_ORGANIZATION] PRIMARY KEY CLUSTERED 
(
    [ID] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, FILLFACTOR = 80) ON [PRIMARY]
) ON [PRIMARY]
GO

ALTER TABLE [dbo].[REL_GROUP_ORGANIZATION] ADD  CONSTRAINT [DF_REL_GROUP_ORGANIZATION_SEQ]  DEFAULT (NEXT VALUE FOR [dbo].[REL_GROUP_ORGANIZATION_SEQ]) FOR [ID]
GO

ALTER TABLE [dbo].[REL_GROUP_ORGANIZATION]  WITH CHECK ADD  CONSTRAINT [FK_REL_GRP_RGANIZATIN_GRP_ID] FOREIGN KEY([GROUP_ID])
REFERENCES [dbo].[RAPID_GROUP] ([ID])
GO

ALTER TABLE [dbo].[REL_GROUP_ORGANIZATION] CHECK CONSTRAINT [FK_REL_GRP_RGANIZATIN_GRP_ID]
GO

ALTER TABLE [dbo].[REL_GROUP_ORGANIZATION]  WITH CHECK ADD  CONSTRAINT [FK_REL_GRP_RGANZATN_RGANZATN_D] FOREIGN KEY([ORGANIZATION_ID])
REFERENCES [dbo].[LU_ORGANIZATION] ([ID])
GO