I'm not sure, but you may be referring to this article:
(though the researchers don't specifically mention Rebif). But keep in mind that only those that had the neutralizing antibodies had problems, and this is a relatively small percentage of people (even in this study it was only 25%). Also, keep in mind that this is only one small study, and you can design a study and interpret the data to show almost anything. That's why they always end with a statement like:
Prospective studies are warranted to confirm these results.
But, any concerns you have are valid, and you should discuss them with the neuro.