Final answer:
The client was not allowed to vote his proxy for a specific stock because the shares from his recent purchase were failing settlement.
Step-by-step explanation:
The likely reason the client was not allowed to vote his proxy for a specific stock is option d. The shares from his recent purchase were failing settlement. When a stock purchase fails to settle, it means that the buyer has not fulfilled the financial obligations of the purchase transaction. This can happen for various reasons, such as insufficient funds or incorrect paperwork.
In this case, the client's recent purchase of shares did not go through the settlement process successfully, which resulted in him not having the necessary ownership rights to vote the proxy for that stock.
To rectify the situation, the client should contact his broker or the institution where he made the purchase to resolve the settlement issue before he can exercise his voting rights.