Update troubleshooting.md

Author: nikhilkaul-msft

articles/chaos-studio/troubleshooting.md

@@ -129,4 +129,10 @@ From the **Experiments** list in the Azure portal, select the experiment name to
 
 This error might happen if you added the agent by using the Azure portal, which has a known issue. Enabling an agent-based target doesn't assign the user-assigned managed identity to the VM or virtual machine scale set.
 
-To resolve this problem, go to the VM or virtual machine scale set in the Azure portal and go to **Identity**. Open the **User assigned** tab and add your user-assigned identity to the VM. After you're finished, you might need to reboot the VM for the agent to connect.
+To resolve this problem, go to the VM or virtual machine scale set in the Azure portal and go to **Identity**. Open the **User assigned** tab and add your user-assigned identity to the VM. After you're finished, you might need to reboot the VM for the agent to connect.
+
+## Problems when setting up a managed identity
+
+### When I try to add a system-assigned/user-assigned managed identity to my existing experiment, it fails to save. 
+
+If you are trying to add a user-assigned or system-assigned managed identity to an experiment that **already** has a managed identity assigned to it, the experiment fails to deploy. You need to delete the existing user-assigned or system-assigned managed identity on the desired experiment **first** before adding your desired managed identity.