Class "acf_options_page" not found

You do not the Options Page plugin for this to work. I’ll work on a patch to fix this, in the meantime, replace the file code with this. (simply adding the class_exists() check)

if (class_exists('acf_options_page'))
{

class umt_acf_options_page extends acf_options_page
{
	var $umt;

	function __construct($parent)
	{
		$this->umt = $parent;

		// Setup Addon
		global $acf;
		if (isset($acf->options_page))
		{
			// call the original acf_options_page constructor
			parent::__construct($acf);

			// setup initiation procedure
			add_action('init',array($this,'init'),99);

			// setup register options page init
			add_action('admin_init',array($this,'umt_admin_init'));
		}
		else
		{
			trigger_error("ACF Options Page support for Ultimate Metabox Tabs has become broken. Please contact the developer. For now, disable the extension.");
		}
	}

	function init()
	{
		global $acf;
		// remove the admin menu hook
		remove_action('admin_menu', array($acf->options_page,'admin_menu'));

		// override the original options page
		$acf->options_page = $this;
	}

	function admin_body_class($classes)
	{
		$classes = str_replace(" umt_no_margin","",$classes);
		return $classes;
	}

	function umt_admin_init()
	{
		// register metatabs page
		umt_register_settings_page($this->umt_slug,$this->umt_name);
	}

	function admin_head() {
		$this->umt->metatab_load_settings_page($this->umt_slug);
  		$this->umt->admin_head();

		add_filter('admin_body_class',array($this,'admin_body_class'));

		parent::admin_head();
	}

	function admin_print_scripts() {
		$this->umt->metatab_load_settings_page($this->umt_slug);
		parent::admin_print_scripts();
		// remove original filter, only if on the 'options page'
		remove_filter('richedit_pre', array($this->umt,'richedit_pre'),99);

  		$this->umt->admin_print_scripts();
	}

	function admin_print_styles() {
		parent::admin_print_styles();
		$this->umt->admin_print_styles();
	}

	function html()
	{
		parent::html();
		// append metabox tabs
		$this->umt->metatab_create();
	}
}
}