This message is caused by material that is not supported by Corona being present in the scene. Corona will render such material with red warning-labeled material.
The scene contains one or more materials that are not supported by Corona. This often happens if the objects with Corona-incompatible materials are loaded into the scene from an external source (for example by merging scenes). See this list for all materials that Corona supports.
Remove offending material from your scene and replace it with Corona-compatible material - this can be easily automated using the Converter Script.
Unsupported material displayed in rendered image