As Coptic Orthodox, we do not agree with many of the dogmas of the Roman Catholic Church, such as, The nature of our Lord Jesus Christ, The Filioque Controversy, Purgatory, Infallibility of the Pope, Immaculate Conception of the Blessed Virgin, Primacy of St. Peter, Fasting, and many others things. This is why we cannot say that we have the exact faith and therefore they cannot partake of the Holy Eucharist at our church.  To read more about the differences between the Orthodox and the Catholic Church check this website " http://www.suscopts.org/resources/literature/orthodox-faith/difference-between-catholicism-and-orthodoxy/ "  where you will find the biblical references on which the Coptic Orthodox Church has based her stance and traditions.