Many to many cardinality association not enabled with composed key entity

Hi, I created 6 entities from a Ms-Sql Server 2005 legacy database with the generate model capability (Cuba Studio 6.7.5).
One of these tables has a composed key:

CREATE TABLE [dbo].[CONTRAC1](
[CteCd] [int] NOT NULL,
[CteLnCd] [smallint] NOT NULL,
[AgDuCd] [smallint] NULL,
[ArtCd] char NULL,
[ProcCd] [smallint] NULL,
[CteLnPrB] [decimal](12, 4) NULL,
[CteLnPrN] [decimal](12, 4) NULL,
[CteLnDte] [smallmoney] NULL,
[CteLnDtOut] [datetime] NULL,
[DiCd] [smallint] NULL,
[CteLnSpg] char NULL,
[CteLnObs] char NULL,
[CteLnStat] [smallmoney] NULL,
[CteLnDtPre] [datetime] NULL,
[CsCd] [smallint] NULL,
[NavCd] [smallint] NULL,
[TranCd] [smallint] NULL,
[CteLnFPgCd] [smallint] NULL,
[CteLnTQN] [money] NULL,
[CteLnTQB] [money] NULL,
[CteLnRefP] char NULL,
[CteCmd] char NULL,
[CteDivCot] [decimal](14, 6) NULL,
[CteDivDtCo] [datetime] NULL,
[CteVerCot] char NULL,
[CteLlCd] char NULL,
[CtePreuTot] [money] NULL,
[CteRutaGes] char NULL,
[CteLnMesDt] [smallint] NULL,
[CteLnAnyDt] [smallint] NULL,
[CteLnCanc] char NULL,
[CteFabrica] char NULL,
[CteLnHighC] char NULL,
[CteQuinzPr] [smallint] NULL,
[CtefLnInPr] [decimal](12, 4) NULL,
[fCteLnQual] char NULL,
[CteLnIniTQ] [money] NULL,
[CteLnDtAvi] [datetime] NULL,
[CteLnComAg] [smallmoney] NULL,
[CteLnNFacP] char NULL,
[CteLnDtFac] [datetime] NULL,
[CteLnFacCo] char NULL,
CONSTRAINT [PK_CONTRAC1] PRIMARY KEY CLUSTERED
(
[CteCd] ASC,
[CteLnCd] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]

Then, I wanted to create a new entity from scratch with an attribute defined as a many to many cardinality association with the entity with the composed key. The problem is that the many_to_many cardinality association option is not displayed. If I choose another of the 5 other entities generated with no composed key, the many_to_many option is displayed.

Someone knows if there is any limitation with the many to many cardinality association when the entity has a composed key? Is there a work around?

Thanks in advance

Solved by changing the entities dessign.