"Cnut or Knud, in one syllable, is this King’s true name, and the best Latin form is Cnuto, according to the usual way of Latinizing Scandinavian names. The form Canutus seems to have arisen from Pope Paschal the Second’s inability to say Cnut. The later King Cnut, the supposed martyr, was therefore canonized by him as “Sanctus Canutus”. [Æthelnoth, author of a Life of Saint Cnut,] an English monk settled in Denmark, thinks the lengthening of the name a great honour, and compares it with the change from Abram to Abraham; but he somewhat inconsistently cuts down his own name to Ailnothus."
I don't know if this is true, but it is amusing.