A sighted persion is given a much larger piece of information at a time than a blind person, i.e. an image versus a string of words. When the error messages are on a different page than the form, the sighted person can read an error message, go back to the previous page with the form, scan the page for the desired field with the error and fix the error. For many blind users, this arrangement can be much more cumbersome because they cannot scan over a page. They may have to start at the beginning of the page and have the page read to them till they get to the desired field. This process is frequently inefficient.
Some blind people can compensate in certain ways.
For example, some blind people can significantly increase the rate at which a web page is read which reduces the amount of time needed to get to the field with the error. Another way is to use any text search mechanism available, e.g. search for first name. Unfortunately, this mechanism is not always reliable. For example, suppose that there are two fields on a form for the first name each of the spouses in a marriage. Looking for the appropriate first name field can be a problem.