an error in distance measurement from source to detector is the source of the problem

That's narrower than what I'm offering. For example, the Science 20 article points out a possible error in the refraction index of the Gran Sasso light guide. Your side of the bet (if you still want to take it) could be rephrased as "In whichever explanation is found, they had the source-detector distance and all time offsets right (or knowingly lied about them)".

Also I reserve the right to renegotiate if the exchange rate goes weird before either of us hears the explanation.