There is a book called Communicatio in Sacris. It is the only book in the world that documents, details, and quotes why the Roman Catholic Church prohibits Catholics from intercommunicating  (communicate mutually) with protestants or any non- Catholic. Communicatio in Sacris can be found at the following website http://www.sspxarchbishopmarcellefebvre.com/communicatio-in-sacris/       

                                                                                                                                      One example of this is communion. Catholics are strictly forbidden to take communion at a Protestant church.  Biblically, the purpose of communion is to remember the death of Jesus Christ and the new covenant and to “proclaim” His sacrifice by means of illustration (Matthew 26:28; Luke 22:19; 1 Corinthians 11:26). In a Catholic Church, the purpose is entirely different. When a person receives communion in a Catholic Church, the priest says, “The Body of Christ,” and the communicant responds, “Amen” in agreement. This signifies a belief in transubstantiation. The vast majority of Protestants strongly disagree with the Catholic understanding of the Lord’s Supper, and it would be dishonest to say, “Amen.” 

There are just too many disagreements between the RCC and Protestants over how a Christian should live and worship.