I have Illustrator CC 2015 (19.1.0) and fresh downloaded SDK (AI_CC_2015_SDK_Mac_44_0.dmg). XCode Version 6.4 (6E35b), OS X 10.5 El Capitan.
Sample plugins don't show their panels from Window menu. I've tried FreeGrid, Tutorial, SnippetRunner. When I choose Window->SDK->SnippetRunner - nothing happens. Only EmptyPanel shows its controls (panel and control bar), but it has some strange rectangle with shadow over it, see the screenshot. What's it all about? Any ideas?
Exploring other samples:
DrawArt demo explanation says "This sample is a CS Extension; to run it, choose Window > Extensions > DrawArt.", but I have no Extensions menu under the Window.
LiveDropShadow works well, as it has no panels to show.
MarkedObjects seems to be working but again - when I choose "Window > SDK > Marked Objects" menu - nothing happens.
MenuPlay, MultiArrowTool are working but they don't need panels.
ScriptMessage - I counldn't understand where to find that panel.
StrokeFilter - when I choose Object > Filters > Additional Filters > Dash or Wave - I get an error window with text "SDK_ASSERT File=/...local path.../samplecode/StrokeFilter/Source/StrokeFilterFlashController.cpp Line=75", which is somehow also about the plugin's panel.
TransformButtons - when I choose Window > SDK > Transform Buttons > Show Transform Buttons Dialog - nothing happens.
TwirlFilee - WHOA! This is the only plugin from samplecode folder which actually shows up its panel and fully works!
Webter - Window > SDK > Webter - shows nothing.
You need to build the equivalent *UI projects using Flash Builder.