Mr Physical Sky

[mcvl72]

I'm new to 3ds Max, 2009 Design to be precise. Trying to understand how mr physical sky works. I'm trying to apply a "custom background image" (rollouts), but when I render my scene all I get is black ground, black sky and a thin light at the horizon line. Am I missing something? I've been reading from the help files and any free stuff on the net but nothing is being revealed to me as to the issue. Does anybody have some thoughts on this?

Thanks!