Hello John
It is because there was an update site with that old URL created in the past. I will release version 3.0.1 later today. When you update to that latest version, the system will, the system will remove that old update site and the error will be gone
Or you can go to Extensions -> Manager, find and disable the update site with that URL and the error will be gone too. Note that you need to disable the update site with
www.joomdonation.com/updates/membershippro.xml URL but keep the update site with
joomdonation.com/updates/membershippro.xml
(In short, disable/delete the one with www in the URL, keep the one without www)
Tuan
