I can't guarantee that this was the reason, but it fixed it when I did it, so I guess that qualifies it as an answer. Most *.xml files (including the layout files in the layout component of the resources) have the following as the first line:

<?xml version="1.0" encoding="utf-8"?>

However, once I removed this from the attrs.xml, colors.xml, strings.xml & styles.xml files in the values directory of the resources, everything seemed to work (the resources were regenerated & I was able to access the resources from the projects that referenced them). This didn't fix the CS8700 Multiple analyzer… error mentioned in my original post, but I don't think they were ever really related anyway, so that's probably better for another question. I did not remove this line from any other *.xml files (only from files with a root tag of <resources>). I don't know why this fixed it, but hopefully it will fix it for everyone else as well. Good luck!