What is a dual relationship in the context of human services? Why are dual relationships discouraged or forbidden by most codes of ethics?

No discussion of ethics in the Human Services profession is complete without a discussion of dual relationships?

What is a dual relationship in the context of human services?
Why are dual relationships discouraged or forbidden by most codes of ethics?
Give some examples of different types of dual relationships.
Discuss how the formation of dual relationships can be discouraged.
Discuss how dual relationships can be eliminated when they do occur.