error: Error parsing XML: not well-formed (invalid token) ...?

I had this problem, and when I had android:text="< Go back" it had the correct syntax highlighting, but then I realized it's the < symbol that is messing everything up.

It means there is a compilation error in your XML file, something that shouldn't be there: a spelling mistake/a spurious character/an incorrect namespace.

Your issue is you've got a semicolon that shouldn't be there after this line:

  android:text="@string/hello";