The problem with layout rendering is the most popular bug in issues tracker at BitBucket. I am well aware of that and recently I made a few changes to again make it more robust and basically attempted to be able to render a layout with some reasonable defaults without manual setting. Still there are assumptions like:
it expects that the project is built (to load identifiers from generated R.java and possibly project/library widgets), it needs to be able to parse AndroidManifest.xml from project, it will guess what is the best target platform to use for rendering and will use a default device (Nexus 4), its state (PORTRAIT), theme and so on. You can give it another try. Reminder: the AUC link is now http://nbandroid.org/updates/updates.xml.
Unrelated to that is that I was able to improve tests to run multiple times again different versions of Android target platforms. This is nice as it helps to make sure that new updates do not break existing functionality. This is done using AbstractMultiTestRunner from Gradle project - pretty smart class.