VM deployment errors are captured in activity logs. You can find lab VM activity logs under Audit logs or Virtual machine diagnostics on the resource menu on the lab's VM page (the page appears after you select the VM from the My virtual machines list).
Sometimes, the deployment error occurs before VM deployment begins. An example is when the subscription limit for a resource that was created with the VM is exceeded. In this case, the error details are captured in the lab-level activity logs. Activity logs are located at the bottom of the Configuration and policies settings. For more information about using activity logs in Azure, see View activity logs to audit actions on resources.