This can be due to many issues, and it's a known one. Try clicking slightly below the close button in the SF window, and it should close properly. After that SF should be working again

Right, my bad! You'll have to drag a cubemap in onto the node from the project browser for now. I'll look into that :)

I've never been able to reproduce this! Which Unity version are you running? And are you using Free/Pro?

Yep, Light Attenuation is the way to do that :)

Could you elaborate "Add shadows"? Cast shadows or receive shadows?

Shadowed Alpha clipping/Transparency is messy, it's a known issue :)