Final answer:
The scientist did not make an error regarding the relation between radiation and the Big Bang theory; rather, it was the correct prediction and subsequent discovery of the Cosmic Microwave Background radiation that supported the theory.
Step-by-step explanation:
The error that the scientists made regarding the radiation and the Big Bang theory is not explicitly mentioned in the provided information. However, from the historical context given, it can be inferred that scientists originally had to predict the presence of Cosmic Microwave Background (CMB) radiation prior to its discovery. After the discovery, some scientists were skeptical and had different interpretations, but the predominant error that many may have assumed was that this radiation was not detectable or related to the Big Bang. It was George Gamow and his collaborators who predicted that if the Big Bang occurred, there should be remnant blackbody radiation in space with a temperature of about 7 K. In 1964, Penzias and Wilson detected what we now recognize as the CMB, the afterglow of the primeval fireball from the Big Bang, which aligned remarkably well with predictions.
Many subsequent experiments confirmed Penzias and Wilson's discovery, which eventually led to them receiving the Nobel Prize in 1978. The CMB is the most perfect blackbody spectrum ever detected and provides compelling evidence of the universe's creation in a gigantic explosion. Thus, the correct assertion is that the CMB radiation is remnant of the Big Bang, rather than causing it or being unrelated to it.