If this is a map, it could mean a problem with the lighting, texturing, geometry, or layout; try the Cube Wiki for tips on using the engine. Should it be some other form of content, then it may need to be elaborated upon to be worth something.
The layout of a map is among the most important parts of a winning design, try making sure exotic geometry is removed or clipped and the level is open and free of dead-ends or unexplained phenomena.
Refer to the Packaging Guide for information on how to fix this.