If you are currently using the SQL Server Connector to interface with your Azure Key Vault, please make sure your version is updated to the latest Public Preview refresh version which was released in August. The previous version released in January will be discontinued after October 31, 2015. This is to align all applications with the newest Azure Key Vault REST API since Azure Key Vault is now generally available.
Not sure what version of the SQL Connector you have? You can check the property of the Microsoft.AzureKeyVaultService.EKM.dll under the SQL Connector program file to see if it looks like the screenshot below, which is the most up-to-date version.
For those unfamiliar with the SQL Server Connector, it enables SQL Server encryption to use the Azure Key Vault as an Extensible Key Management (EKM) module for more secure key protection.
Learn more about the SQL Server Connector for Azure Key Vault by visiting the Azure Security’s blog post on the SQL Server entering public preview.
The setup instructions for Extensible Key Management using SQL Server Connector and Azure Key Vault can be found on its MSDN documentation page.