Let me start by acknowledging that I did find a similar question on here but there was only one answer and that answer did not apply in my situation, so...
I am just
Is http://schemas.android.com/apk/res/android
alive?
The XML editor will try to download the XML Schema to validate the XML. If the site is down or the XML schema is damaged, this could cause these errors.
Try to download the schema and add it to your "xml catalogue" (search in your Eclipse preferences) to avoid this problem.