Just as in the real life, there may be a lot of reason why that particular coach will not sign for your team. Your team may not be reputable enough in FM11, or your team is a rival of a club that the coach played (or coached) before or the coach simply does not want to go to your country. The best option in FM2011 is... sign a different coach.
Oh thank you for the reply. That's all good then. Just wanted to know if it is a bug or intentional. Thanks again.