[nerbert]

I would restore your file includes/class_core.php back to original and create this plugin for fetch_template_start:

 
		if (!$fetched)
		{
			if (isset($vbulletin->templatecache["$template_name"]))
			{
				$template = $vbulletin->templatecache["$template_name"];
			}
			else
			{
				self::$template_queries[$template_name] = true;
				$fetch_tid = intval($templateassoc["$template_name"]);
				if (!$fetch_tid)
				{
					$gettemp = array('template' => '');
				}
				else
				{
					$gettemp = $vbulletin->db->query_first_slave("
						SELECT template
						FROM " . TABLE_PREFIX . "template
						WHERE templateid = $fetch_tid
					");
				}
				$template = $gettemp['template'];
				$vbulletin->templatecache["$template_name"] = $template;
			}
		}

		if (!isset(self::$template_usage[$template_name]))
		{
			self::$template_usage[$template_name] = 1;
		}
		else
		{
			self::$template_usage[$template_name]++;
		}

		/////////($hook = vBulletinHook::fetch_hook('fetch_template_complete')) ? eval($hook) : false;

		return $template;

That code is a straight copy/paste out of the file itself with the fetch_template_complete hook commented out (Idon't think you can have a hook in a plugin). Now the plugin code finishes the function (method, for you purists) and everything should run.

Now try playing around with commenting out the database query and replacing it with file_get_contents(). You should actually open, lock, read and unlock the file instead of just reading it with f_g_c()