Update 02-cognitive-services-security.md

This fixes MicrosoftLearning#204

Instructions/02-cognitive-services-security.md

@@ -124,9 +124,9 @@ First, you need to create a key vault and add a *secret* for the cognitive servi
 
 To access the secret in the key vault, your application must use a service principal that has access to the secret. You'll use the Azure command line interface (CLI) to create the service principal, find its object ID, and grant access to the secret in Azure Vault.
 
-1. Return to Visual Studio Code, and in the integrated terminal for the **02-cognitive-security** folder, run the following Azure CLI command, replacing *<spName>* with a suitable name for an application identity (for example, *ai-app*). Also replace *<subscriptionId>* and *<resourceGroup>* with the correct values for your subscription ID and the resource group containing your cognitive services and key vault resources:
+1. Return to Visual Studio Code, and in the integrated terminal for the **02-cognitive-security** folder, run the following Azure CLI command, replacing *<spName>* with a unique suitable name for an application identity (for example, *ai-app* with your initials appended on the end; the name must be unique within your tenant). Also replace *<subscriptionId>* and *<resourceGroup>* with the correct values for your subscription ID and the resource group containing your cognitive services and key vault resources:
 
-  > **Tip**: If you are unsure of your subscription ID, use the **az account show** command to retrieve your subscription information - the subscription ID is the **id** attribute in the output.
+  > **Tip**: If you are unsure of your subscription ID, use the **az account show** command to retrieve your subscription information - the subscription ID is the **id** attribute in the output. If you see an error about the object already existing, please choose a different unique name.
 
  ```
  az ad sp create-for-rbac -n "api:https://<spName>" --role owner --scopes subscriptions/<subscriptionId>/resourceGroups/<resourceGroup>