In function phpbb_require_updated() we have too parameters $path, $optional = false, and when new path is not available we try looking for file in old path and it has

if (file_exists($new_path))

	{

		require($new_path);

	}

	else if (!$optional || file_exists($old_path))

	{

		require($old_path);

	}

it should rather be like this

if (file_exists($new_path))

	{

		require($new_path);

	}

	else if (!$optional && file_exists($old_path))

	{

		require($old_path);

	}

NOTE the && in else if (!$optional && file_exists($old_path))
this would prevent from error if file is not found.