if (pEnvelopeFeedback != null)

                        {                          

                           //   EnvelopeClass();

                            IEnvelope pEnvelope = new EnvelopeClass();

                            ISpatialFilter pSpatialFilter = new SpatialFilterClass();

                            pEnvelope = pEnvelopeFeedback.Stop();

                            pSpatialFilter.Geometry = pEnvelope;

                            pSpatialFilter.SpatialRel = esriSpatialRelEnum.esriSpatialRelContains;

                            pSpatialFilter.GeometryField = GeometryColumn;

                            ISelectionSet2 pselset;

                            IFeatureCursor pFeaturecursor;

                            pFeaturecursor = pFeatureClass.Search(pSpatialFilter, false);

                            int FeatureCount;

                            FeatureCount = pFeatureClass.FeatureCount(pSpatialFilter);

                            //MessageBox.Show(FeatureCount.ToString());

                            IFeature pFeature;

                            pFeature = pFeaturecursor.NextFeature();

I have a message about these implementations Ienvelope and ISpatialFilter for both the message said : interop type .....can not be embedded. Use the applicable interface instead??

I checked other implementation and this is the correct way to do it.