Like Twenty20 I agree you should speak to the person and you should ask for some concrete examples.
In my first very job I had a boss who did this and it absolutely drove me mad. She'd ask you to do something in the vaguest terms and then complain that you hadn't done exactly what she asked. When you complained that she didn't specify what she wanted she seemed to think that you should be able to read her mind! If your employees are always seeming to get things wrong or are constantly having to ask you to repeat your instructions maybe you are not being clear. Perhaps you should think through what you are going to say to someone first to see whether there is anything ambiguous in what you are saying .
Sorry I don't understand your question. (Sorry , could not resist that). When you next give someone a decision/instruction you should ask them to repeat it back to you to make sure they have understood
I agree. Ask them to repeat the instruction back to you because their intrepretation could be different to yours although the words are technically correct.
Don't just ask "do you understand" because most people will just say yes to avoid looking stupid/embarrassed.
Another key point is to present the information in a logical order. Don't jump back and forth from point to point and keep it as short as possible without any "waffle"