This error warns you about missing PHP extension that is needed to properly run the Post Affiliate Pro 4. Imgettftext is a part of GD extension so please check if your PHP supports it or if it has the newest extension (gd2). You will also need TTF extension to make it working.
If you do not know how to do this, just try to ask your hosting if they can enable these extensions for you. They will probably need to recompile PHP to enable both TTF and GD extension.