My advice is don't drag and drop, look at how it is used in existing features and follow the example in your own feature code. I have never used the toolbox or drag and drop at all in my work and I can't really offer any advice or support on using it except don't use it, pretend it doesn't exist. Don't bother with design view in VS, it doesn't work very well to begin with and works even less well in mojoPortal because of the way our skinning model works css is resolved differently at runtime than design time. Just use source view and work directly with the markup and control declarations. Use the web browser to see the result.