IANAL, but in the US, at least, a mistake like this does not invalidate a contract. As long as the intent of a contract is clear, the courts will still enforce it.
What a mistake like this CAN do is make the contract ambiguous, and give one of the parties an opportunity to try to convince a judge that their interpretation is what was intended, or at least, that they reasonably believed that that was what was intended.
It's hard to see how someone could plausibly claim ambiguity in this example. I doubt any judge would buy an argument that "consultant" here means "company" and not "contractor". But one can easily imagine a contract where the parties are not clearly identified, and that has a clause like, "the Contractor shall pay all shipping expenses", and both parties claim that "the Contractor" means the other guy.
While judges have made a lot of crazy decisions over the years, especially when politics is involved, most of the time their rulings make some sort of sense. Unless the judge has some reason to be biased against one party or the other, he's not going to throw out a contract just because of one inconsistent word usage. Contracts are written by human beings. I'm sure lots of contracts contain errors of one sort or another, and the longer and more complex the contract is, the more likely it's going to have this kind of mistake.