You plan to back up an Azure virtual machine named VM1. You discover that the Backup Pre-Check status displays a status of Warning. What is a possible cause of the Warning status? 

Answer options:

A. VM1 is stopped.
B. VM1 does not have the latest version of the Azure VM Agent (WaAppAgent.exe) installed.
C. VM1 has an unmanaged disk.
D. A Recovery Services vault is unavailable.

B

The Warning state indicates one or more issues in VM`s configuration that might lead to backup failures and provides recommended steps to ensure successful backups. Not having the latest VM Agent installed, for example, can cause backups to fail intermittently and falls in this class of issues. Reference: https://azure.microsoft.com/en-us/blog/azure-vm-backup-pre-checks/