A lexicographic error means that something is not in the right order like when you try to arrange your toy blocks but they aren't in the right order. In other words, it's like mixing up the alphabet letters. Just like how you know the Alphabet song, where A comes first, B comes second, and so on, your computer also has a set of rules to determine the correct order of things.
For example, when you make a list of words on your computer, it follows a certain order, like putting the words starting with A first, and then those starting with B, and then C, and so on. If your computer made a mistake, it might put a word starting with B before a word starting with A, which would be like singing the Alphabet song but starting with the letter D instead of A.
This can cause problems, especially when it comes to sorting things. For example, if you have a list of names, and the computer doesn't sort them in the right order, then it might be hard to find the name you're looking for. So it's important to make sure everything is in the right order.