Premise: The client (who chose the producer) should protect the producer if and when others from the company are participating in reviews. Protection means standing up for the producer and defending the structure and creative that he or she approved.
If you've ever been in a review by committee, you know the paralyzing fear it can cause you. The committee has not been a part of the process, so their reviews will be necessarily out of left field. The only person who knows what has transpired to get to this point is your direct client.
So the client needs to step up when necessary.
This means defending your your creative plan, script, or finished product to the outsiders. Sometimes this isn't easy for the client, but it is necessary.
One way to help your client do this is to set the scene before the actual presentation. Tell the committee what your goals were, what you wanted to get across, what general approach you took, and why this approach should work. This helps set some boundaries for the review process. Also, let them know that you'd like to keep the first part of the discussion general-- do you like it or not? This will help you by eliciting general comments ("I like it!") that you can use to frame more specific objections later.
Some creatives are very sensitive, and some group discussions may go off the rails. This is where the good client will intercede, protecting the project, allowing for an orderly retreat, so that solutions to legitimate problems can ensue without any hurt feeling, bruised egos, or shouting matches.
Finally, there may be unwarranted budget discussions (you have a signed contract, right?) Committee members (or even superiors to your client) may question how much is being spent. This is where a simple statement from the client ("The budget has been approved") can be followed up by you with an explanation of what goes into making a video, if it comes to that.