FYI:

I changed the nexus value in the engine command line using this syntax:
-NX 80
...and that did the trick. I'm now able to cycle through all 28 sky models I have, but it ends up taking up a large amount of virtual memory (which is what the command line above does - tells the engine to reserve 80 meg of virtual memory on the hard drive).

Does anyone know how to clear the virtual memory??