hibernate保存主键出错！

public String save(Imibtsp imibtsp, Imibmsp imibmsp, Imlcmsp imlcmsp)
            throws net.sf.hibernate.HibernateException {        Transaction t = null;
        Session s = null;
        try {
            s = getSession();
            t = this.beginTransaction(s);            s.update(imlcmsp);
            s.update(imibtsp);
            s.update(imibtsp.getEmtsctp());
            System.out.println(imibmsp.getMspId().getIbno());
            System.out.println(imibmsp.getMspId().getBrno());
            String rtn = (String) s.save(imibmsp);  //这个地方报错            this.commitTransaction(t);            return rtn;
        } catch (HibernateException e) {
            if (null != t)
                t.rollback();
            throw e;
        } finally {
            closeSession();
        }
    }
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xml文件：
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd" ><hibernate-mapping package="com.witsoft.hibernate">
<class name="Imibmsp" table="IMIBMSP"> <composite-id class="ImibmspPK" name="MspId">
<key-property column="IBNO" length="16" name="Ibno"
type="string" />
<key-property column="BRNO" name="Brno" type="string" />
</composite-id> <property column="ADL2" length="35" name="Adl2" not-null="false"
type="string" />
<property column="ADL4" length="35" name="Adl4" not-null="false"
type="string" />
<property column="TDDT" length="8" name="Tddt" not-null="false"
type="string" />
<property column="DRCB" length="1" name="Drcb" not-null="false"
type="string" />
<property column="RMTP" length="1" name="Rmtp" not-null="false"
type="string" />
<property column="LCNO" length="16" name="Lcno" not-null="false"
type="string" />
<property column="ULTP" length="1" name="Ultp" not-null="false"
type="string" />
<property column="TMAM" length="53" name="Tmam" not-null="false"
type="java.lang.Float" />
<property column="CRAC" length="36" name="Crac" not-null="false"
type="string" />
<property column="PYTP" length="1" name="Pytp" not-null="false"
type="string" />
<property column="DFAM" length="53" name="Dfam" not-null="false"
type="java.lang.Float" />
<property column="PYDT" length="8" name="Pydt" not-null="false"
type="string" />
<property column="NGNO" length="16" name="Ngno" not-null="false"
type="string" />
<property column="IVNO" length="16" name="Ivno" not-null="false"
type="string" />
<property column="UTNO" length="16" name="Utno" not-null="false"
type="string" />
<property column="RNDT" length="8" name="Rndt" not-null="false"
type="string" />
<property column="SGNO" length="16" name="Sgno" not-null="false"
type="string" />
<property column="DUDT" length="8" name="Dudt" not-null="false"
type="string" />
<property column="BLNO" length="16" name="Blno" not-null="false"
type="string" />
<property column="APDT" length="8" name="Apdt" not-null="false"
type="string" />
<property column="ACAM" length="53" name="Acam" not-null="false"
type="java.lang.Float" />
<property column="SAC3" length="5" name="Sac3" not-null="false"
type="string" />
<property column="FNNO" length="16" name="Fnno" not-null="false"
type="string" />
<property column="SUTP" length="1" name="Sutp" not-null="false"
type="string" />
<property column="ADL3" length="35" name="Adl3" not-null="false"
type="string" />
<property column="CKNO" length="10" name="Ckno" not-null="false"
type="string" />
<property column="ARDT" length="8" name="Ardt" not-null="false"
type="string" />
<property column="SAC2" length="5" name="Sac2" not-null="false"
type="string" />
<property column="RZAC" length="36" name="Rzac" not-null="false"
type="string" />
<property column="CRDT" length="8" name="Crdt" not-null="false"
type="string" />
<property column="RBDT" length="8" name="Rbdt" not-null="false"
type="string" />
<property column="GSTP" length="5" name="Gstp" not-null="false"
type="string" />
<property column="DRMK" length="1" name="Drmk" not-null="false"
type="string" />
<property column="SP20" length="20" name="Sp20" not-null="false"
type="string" />
<property column="CGIT" length="5" name="Cgit" not-null="false"
type="java.lang.Short" />
<property column="TSTP" length="4" name="Tstp" not-null="false"
type="string" />
<property column="ACDT" length="8" name="Acdt" not-null="false"
type="string" />
<property column="BEDT" length="8" name="Bedt" not-null="false"
type="string" />
<property column="INNO" length="2" name="Inno" not-null="false"
type="string" />
<property column="EVNO" length="16" name="Evno" not-null="false"
type="string" />
<property column="SAC1" length="5" name="Sac1" not-null="false"
type="string" />
<property column="TENR" length="5" name="Tenr" not-null="false"
type="java.lang.Short" />
<property column="EXR2" length="53" name="Exr2" not-null="false"
type="java.lang.Float" />
<property column="RJDT" length="8" name="Rjdt" not-null="false"
type="string" />
<property column="IBCY" length="2" name="Ibcy" not-null="false"
type="string" />
<property column="CLNO" length="13" name="Clno" not-null="false"
type="string" />
<property column="NGBK" length="11" name="Ngbk" not-null="false"
type="string" />
<property column="IBST" length="1" name="Ibst" not-null="false"
type="string" />
<property column="STCD" length="1" name="Stcd" not-null="false"
type="string" />
<property column="BPDT" length="8" name="Bpdt" not-null="false"
type="string" />
<property column="IBAM" length="53" name="Ibam" not-null="false"
type="java.lang.Float" />
<property column="NGCH" length="53" name="Ngch" not-null="false"
type="java.lang.Float" />
<property column="IVAM" length="53" name="Ivam" not-null="false"
type="java.lang.Float" />
<property column="PADT" length="8" name="Padt" not-null="false"
type="string" />
<property column="ADL1" length="35" name="Adl1" not-null="false"
type="string" />
<property column="PYAM" length="53" name="Pyam" not-null="false"
type="java.lang.Float" />
</class>
</hibernate-mapping>