The default Nexuiz demos play just fine, but when I load any demos I have created, the levels fail to load (visually). Everything is black. The characters, weapons, and items all load correctly though. Help!

Edit:
In the console, it first tells me that the level (.bsp) failed to load, followed by: Model x1 Not Found, Model x2 Not Found, all the way through whatever number Nexuiz decides not to load.

Maybe it's a demo in a custom map. What map is the demo on?

The demo will not work right if :
A. you don't have the map
B. you have it but it's in the dlcache

I'm assuming your issue is B. In that case move the map from the dlcache to the data directory.

Maps that you download from servers are stored in the dlcache directory. To access them the same way that you access the maps that come with the game, you can do one of two things:

1) Just move the pk3 file into the data directory.

OR

2)Use this command on the command line: curl --pak <file.pk3>

Replace <file.pk3> with the full name of the pk3 map file.
E.g. curl --pak capturecity-v2r1.pk3

You guys are great. Problem solved.

I came from a Halflife background. I never had to move any demo files there! :]

Thx bunches!