Yes, only that section, but if that's the OW, then ALL components of that section. I had a student get a "brain cramp" on the rescue assessment. This was my only student to not pass the I.E. the first take. He knew it when it happened, but got so nervous that he made another error on the retake.
Was he competent? Yes. Did he have test anxiety? Yes. Would I let him teach my family? Yes.
You can retake 2 sections without redo-ing the entire exam. After that, it is an entire retake. I'd say that if you have that much of a problem either your CD didn't do you justice, or you need to address testing methodologies, because not being able to show the examiner what you know can be very expensive.
I will say that I debrief my candidates and modify my IDCs accordingly. If I find that there was a potential weakness in a student that I could have shored up beforehand, I modify my teaching presentations/techniques. Over time I've gotten a pretty comprehensive set of review methods to ensure passing the academics, and now I have an iron clad way of prepping for the rescue diver (seems that candidates get nervous on this - the same way new OW divers get wound up over the mask skills).
Anyway. Joe-Diver is right. If either you or the CD feel you've got weaknesses, you shouldn't be attending the IE until those are resolved.