Teve o mesmo problema. Encontrei isto: ZTIUtility.vbs
If (oTS.SelectSingleNode("//step[@type='BDD_InstallOS']") is nothing) and (oTS.SelectSingleNode("//step[@type='BDD_UpgradeOS']") is nothing) then
E altere para:
If (oTS.SelectSingleNode("//step[@type='BDD_InstallOS' and @disable='false']") is nothing) and (oTS.SelectSingleNode("//step[@type='BDD_UpgradeOS' and @disable='false']") is nothing) then