In which of the following scenarios is a lawyer prohibited from representing a client?

A lawyer is prohibited from representing a client when their interests are directly adverse to another client's interests. This situation creates a conflict of interest, which can undermine the lawyer's duty of loyalty to their clients. The ethical rules require lawyers to avoid situations where their representation of one client may be adversely affected by their responsibilities to another client or their own interests. If a lawyer represents clients with conflicting interests, they may be unable to provide adequate representation to either client, which can lead to a breach of professional conduct standards.

The scenario involving a personal relationship with the client might raise questions about potential bias or undue influence, but it does not automatically prohibit representation unless the relationship interferes with the lawyer's ability to represent the client's interests effectively. Non-payment of fees typically does not automatically disqualify a lawyer from representing a client, although it may affect the lawyer's willingness to continue representation. Lastly, disagreement over legal strategy does not preclude representation; it is common for lawyers and clients to have differing views on how to approach a case, and such disagreements can often be resolved through discussion and negotiation.