The "Bro. Fry" that bro. Mansfield is refering to is bro. H. Fry, author of "Echos of Past Controversys" written as a defense against the formation of the Berean Fellowhsip around 1923.
Bro. Fry is the "bro. --" in the article The Truth Concerning Christ's Offering For Himself First Made A Matter of Fellowship In 1898". He was withdrawn from by his ecclesia in 1898, which is recorded in the Christadelphian Magazine while bro. Roberts was yet alive. After bro. Roberts died, he was brought back into fellowship, in a different ecclesia.
We are sure that bro. Mansfield thought that his patient discussions with an errorist such as Richard Stone was the proper thing to do. We have no doubt that he thought that he could teach the error out of the Central group. But as Paul prophesied he could not, and this is a sobering example of the fruitlessness and danger of this behaviour.
Because these brethren in 1960 refused to follow the sound and Scriptural paths of bre. Thomas and Roberts, 20 years later the error had grown to the point where Richard Stone could publickly give classes on his understanding, convincing many of his wrong ideas, and openly and in writing call the Truth, "error". The Bible prophesied this. It was as inevitable that this should occur as any other Bible prophesy.
At times, in 1978 - 1981 bro. Stone would even circulate the booklet "Echos of Past Controversies" by H. Fry, until it was pointed out to him that bro. Roberts had withdrawn from him over this very belief.