I want to use an Always Encrypted SQL 2016 DB in my .NET app with an Azure Key Vault for storing the encryption keys. I have been following this article so far: 
<https://blogs.msdn.microsoft.com/sqlsecurity/2015/11/10/using-the-azure-key-vault-key-store-provider-for-always-encrypted/>

But I receive an exception when I reach this line of the code provided in the article: 

```
SqlColumnEncryptionAzureKeyVaultProvider azureKeyVaultProvider =
new SqlColumnEncryptionAzureKeyVaultProvider(GetToken);

```

The exception is:

```
Additional information: Method not found: 'Void Microsoft.Azure.KeyVault.KeyVaultClient..ctor(AuthenticationCallback)'.

```

I've checked my references and everythings seems to be in place. The GetToken authentication callback method is also there.

Can anyone help? Thanks.