Imagine how bad Wikipedia would be if original article authors always rejected or rolled back helpful, correct edits made by contributors. It's amusing but sad to think of an equivalent to SE answers on Wikipedia:
One of the most frustrating things about browsing SE sites for answers, as a user, is when there are six different answers, each with a half-truth, various errors, etc. and the most upvoted/accepted answer is wrong or obsolete. People are so afraid of editing someone else's answer, as if it were their "intellectual property", and accidentally "stepping on their toes", that they avoid it and rather post their own answer to add to the clutter instead of helping one answer be the best answer.
Answers on SE are Creative Commons licensed for a very good reason, folks.
And if you think that people conscientiously go back to edit their answers to make the most upvoted / accepted answer better so that users don't have to scroll down pages and pages of answers to get to the best one, that's an extremely optimistic point of view. Maybe you think that you always do that (maybe you always, in fact, do) -- but I can't tell you how many times I've found wrong, incomplete or less-than-ideal answers with a considerable number of upvotes and the accepted answer. In a few instances, the objectively best answer gets voted to the top, but that doesn't always happen, either.
I'm a big proponent of "just edit it" (and, necessarily, "just approve it" if you're a reviewer), working under the assumption that the edit improves the answer without introducing opinion. BTW, I think it's perfectly fine if an answer gives an opinion, and then an edit is made that provides objective evidence supporting the OP's opinion. It's only bad form if an edit to an answer changes the meaning of the OP's opinion, or reverses it entirely.
But a lot of people seem to be under the impression that, just because answers have the OP's gravatar/profile link next to them, they are some kind of an indelible "forum post" that no one but the OP should be able to edit, even helpfully. Both editors and reviewers often seem to have this opinion, and thus, the edits never even get submitted in the first place, or if they do, they get rejected, like yours.
This is a real shame, because it makes SE sites much less accessible and increases the frustration and difficulty of finding good answers. It's only somewhat better than a phpBB forum, because the voting mechanic does tend to (often, but not always) push the most useful answer to the top. But it could be really great if a well-written answer with a typo or an invalid command gets corrected, instead of making someone else "compete" with the original answerer for votes, which might take years of Google searchers coming and upvoting it until it gets more votes than the incumbent - especially if software patches from a vendor have semi-recently broken the original answer's code but a simple edit could fix it.
Unfortunately, as long as SE gives answerers the option (in terms of policy permitting this attitude, not the literal option on UI) to reject an edit on the grounds of "No! It's MINE! I can be wrong if I want to be!", the site will be hamstrung in its usefulness, requiring answer-seekers to run a linear-time algorithm each time they find a potentially applicable question:
for each answer in answers_sorted_by_upvotes_descending
if answer doesn't brick machine and doesn't solve problem then