
IntelliJ is displaying two sets of errors ("URI is not registered (Settings | Languages & Frameworks | Schema and DTD)" & "Attribute xsi: schemaLocation is not allowed here") and has been unable to build. What should I do?

IntelliJ is displaying two sets of errors ("URI is not registered (Settings | Languages & Frameworks | Schema and DTD)" & "Attribute xsi: schemaLocation is not allowed here") and has been unable to build. What should I do?
I solved the same issue by:
ALT+ENTER.Fetch external resource.