So I've given Android Studio a try, because I really like Resharper and noticed that the IDE had some of their functionality built into it. Having now created a default new project, I added a new layout file and wanted to change the existing default 'hello world' example layout, and I got an "URI is not registered" error on the following lines:
You are having this issue because you are at the wrong destination! The correct directory for the Layout resource file has to be under "res-layout" not "res-all-layout"
Let me know if that solved the issue for you... good luck