The problem seems to be that it's trying to get a skinFactory before it tries to get a skinClass... I haven't defined a skinFactory, so why is this exploding? It seems like it should fail elegantly and then try skinClass.
I got past my previous problem- turns out it was some compile settings in my test project. Now the custom components simply aren't finding their skins-
Error: Skin for flexutils_test.ApplicationSkin2._ApplicationSkin_Group1.contentGroup.Badge5 cannot be found.
at spark.components.supportClasses::SkinnableComponent/attachSkin()[E:\dev\4.0.0\frameworks\ projects\spark\src\spark\components\supportClasses\SkinnableComponent.as:632]
at spark.components.supportClasses::SkinnableComponent/validateSkinChange()[E:\dev\4.0.0\fra meworks\projects\spark\src\spark\components\supportClasses\SkinnableComponent.as:405]
I assume you are using FlexBuilder to build and compile and not ant or the comand line correct? If so there are two things you need to check.
1) Where is your defaults.css located? As long as it is in the root of your library's src directory (ie. src/defaults.css) you shouldn't even need to add that compiler option. When it builds a project, FlexBuilder looks for a file named defaults.css in this location and will use it to override the framework version.
2) Go into your project properties -> build path -> assets tab. Make sure your defaults.css file is selected for inclusion.