Simple fix, but you need an extra program to change the WPID file in the .world file before exporting. The WPID is like a product code, and the exchange won't upload more than one. Here's a tut on how to do it. http://customsims3.com/forums/showthread.php?tid=102
Also, here is a tut if you just want to test your world in game, and know it's not ready to share yet on the exchange. http://customsims3.com/forums/showthread.php?tid=127
Edit: Make sure in the name of the world you don't use any punctuation marks like 2.0 You'll be able to open the world once in game, then you'll just get an error message.
