Incorrect pronoun used that has no antecedent either doesn’t refer to any antecedent at all or doesn’t refer clearly to one, and only one, antecedent.

       WRONG: Joe doesn’t like what they play on this radio station.

Who are “they”. There is no antecedent for “they”. On SAT, this sort of usage is an error.

       RIGHT: Joe doesn’t like what the disc jockeys play on this radio station.

Don’t use pronouns without clear, unambiguous antecedents. The antecedent of a pronoun must be a noun.

       WRONG: When you are painting, make sure you don’t get it on the floor.

       RIGHT:      When you are painting, make sure you don’t get paint on the floor.

       WRONG: I’ve always been interested in astronomy and finally have decided to become one.

       RIGHT:      I’ve always been interested in astronomy and finally have decided to become an astronomer.  

       WRONG: Jane quit smoking and, as a result, temporarily put on a lot of weight. It was very bad for her health.

       RIGHT:     Jane quit smoking because it was very bad for her health, and, as a result, she temporarily gained a lot of weight.

       WRONG: He built a fence to stop people from looking into his backyard. That’s not easy.

   RIGHT:      He built a fence to stop people from looking into his backyard. The fence was not easy to build.

*Make sense on your Ear! For Identifying Sentence Errors questions:

If you hear a pronoun that has no antecedent, the pronoun is incorrect.

If you hear a pronoun that could have more than one possible antecedent, the pronoun is incorrect.