Hi Thanet.
Thank you very much for your response. Unfortunately, I think the issue might be with something else.
When I load ReportClasses as well as ReportUtils, it still has the same error. Furthermore, in ReportUtils.php there is the line "require_once 'Google/Api/Ads/AdWords/Util/v201603/ReportClasses.php';", so Utils is including Classes automatically.
"//Load the service, so that the required classes are available.
$user->LoadService('ReportDefinitionService', ADWORDS_VERSIONS);"
I also have this in my code, but my function and the example both throw the selector error.
In contrast, when I load other Services, for instance ManagedCustomerService, the selector works fine.
I've also checked in ReportClasses.php, and the selector class is there. However, the function that calls the class is not being hit.
Thank you in advance for your help or to anyone else who has had a similar issue and has ideas,
Sonya