CPackageSelectGroup::OnPostForm

function OnPostForm()
{
	$wizard = $this->GetWizard();
	$package = $this->package;

	if ($wizard->IsNextButtonClick())
	{
		$groupID = $package->groupID;

		if ($groupID == "")
		{
			$this->SetError(GetMessage("MAIN_WIZARD_ERROR_WRONG_GROUP"), "__groupID");
			return;
		}

		$arGroups = $package->GetTemplateGroups(Array("SITE_ID" => $package->siteID));
		if (!array_key_exists($groupID, $arGroups))
		{
			$this->SetError(GetMessage("MAIN_WIZARD_ERROR_WRONG_GROUP"), "__groupID");
			return;
		}
	}
}