When scheduling an Operations Manager PowerShell script you have to load the powershell snapins.

Insert this in the beginning of your script

_$ServerName = “hostname”

add-pssnapin “Microsoft.EnterpriseManagement.OperationsManager.Client”;

set-location “OperationsManagerMonitoring::”;

new-managementGroupConnection -ConnectionString:$ServerName;

set-location $ServerName;_