Although many faculty survive the tenure review process with unanimous positive votes from their department on up, it is also not unusual for there to be a few negative votes at the stages involving the department or higher level committees, particularly in large departments. That is, although the candidate receives a positive recommendation for tenure, and all votes are a strong majority endorsement of tenure, there might be a few outlier 'no' votes.
Aside from being psychologically painful and perhaps semi- to very devastating to the tenure candidate, despite their ultimate tenure success:
What do these negative votes mean?
There are many possible explanations for the outlier negative votes, but, if this happens to you, one thing these negative votes do not automatically mean is that there are people in your department or on your campus who think you should be denied tenure.
It is possible that the votes mean that, but, from what I've seen, it is more common for there to be a few no votes, even for an overall strong candidate for tenure, for other reasons, including:
The reflexive 'no' vote. Some professors just do this, knowing they will be outvoted, wanting to be outvoted, and proud to be the flag-bearer for impossibly high standards. They don't really want you to lose your job; they just don't want you to think you're so great that you deserve a unanimous positive vote. My advice: Forget the 'no' vote(s), focus on the many 'yes' votes, and don't be a reflexive 'no' voter once you have tenure.
The mini-protest 'no' vote. These voters also don't want you to be thrown out. They think you deserve tenure, but there is something about your record that they don't like, and they are sending you a message about this. This 'something' does not rise to the level of being a cause for tenure denial, so they vote 'no', counting on being in the minority. Ideally, these 'no' voters will indicate what their criticism is (albeit not attributed to anyone in particular) in the letter summarizing the department or committee vote. That way, you will know that one or more faculty had a (small) problem with the number/quality/venues of your publications, think you should put more effort into teaching, or are distressed that you didn't have the right number or type of grants (for example). My advice: Forget the 'no' vote(s), focus on the many 'yes' votes, and try to fix whatever issue has been identified (if you agree that it is a reasonable criticism).
These explanations might not take the sting out of having one or more people vote 'no' in your tenure evaluation, but I think it might be psychologically important for some tenure candidates to know that these outlier 'no' votes do not automatically mean that someone thinks you should be denied tenure. So, if this happens (or has happened) to you, I hope you won't feel (too) paranoid as you wander the corridors or campus byways, that you don't spend hours (years) wondering who voted no, and especially that you won't think about it during faculty meetings, unless it helps pass the time in a more interesting way for you and your suspects, in which case, do whatever it takes to survive.