What does the follwing error means?

Some additional context would be helpful - where and when are you seeing this error message?

An error occurred while trying to write to the entity "CNAM_GC_COLLECTOR_CODE" [id=6c922f6f-e0dc-4c67-94d4-bbfb2a143aad@106711, type=CNAM_GC_COLLECTOR_CODE (id=13984)] (data store: CNAM_GCDS). Details: org.hibernate.NonUniqueObjectException: a different object with the same identifier value was already associated with the session: [CNAMGCCOLLECTORCODEDT45371#0] Data: TypedValue[it=13985,v={{18,PRS_XIM,[Group:4736]},{19,LG1_XJD,[Group:4736]},{20,LG1_XLL,[Group:4736]},{21,PRS_XJD,[Group:4736]},{24,PRS_XLL,[Group:4736]},{27,LG1_XLG,[Group:4736]},{28,LG1_XMD,[Group:4736]},{31,LG1_XFL,[Group:4736]},{<null>,PRS_XLK,[Group:4736]},{<null>,LG1_XLI,[Group:4736]}}]

That's good additional detail but it also doesn't really answer my question of where / when you're seeing it.  What are you trying to do when you encounter this?  In what manner is it being shown to you?

The error is populating, when I am trying to add more than one data to data store, its taking null value for both ids

May need to see your CDT definition - is the ID value set to auto generate, such as below?

      <xsd:element name="id" nillable="false" type="xsd:int">
        <xsd:annotation>
          <xsd:appinfo source="appian.jpa">@Id @GeneratedValue</xsd:appinfo>
        </xsd:annotation>
      </xsd:element>

Is nillable should be "false"?