Sorry, but your post is not clear... who did what to whom?? I will try to answer your post with a lot of "what if's" and "maybe's" in order to save you time of having to repost your clarification....
If you are the Plaintiff, and you are saying that the Defendant has 'rethought' his/her verbal acceptance of a negotiated settlement, then you MIGHT have a hard time trying to prove that a verbal agreement was in fact made, but it MIGHT be do-able depending on the specific circumstances and words used.
Also, if you are the one 'backing out' of a verbal agreement, same situation.
However, all of this is clouded by the attorney issue. If both parties had attorneys, and THEY each agreed, then you (and your attorney) will have a much stronger case against the party who is trying to 'back out', since the attorneys are 'officers of the court' and bound to a higher standard of verbal agreement. (Again, a large part of this is going to be determined by the actual words used in the verbal agreement. It is very simple for two people to THINK that they agree, but then when seeing it in writing, it 'just doesn't look right'. In this case, it could simply be a misunderstanding).
Hope that this is not too confusing.... if it is, please repost your situation with a lot more specifics. You will find that your responses will be much more accurate if you furnish details about the situation.