I also ran into this same error when trying to package one of my projects. Since the error was happening due to a landscape object in a level downloaded from the marketplace, I didn’t have access to the original author of the level, and I didn’t want to spend the time recreating the landscape. So as a workaround, I exported the offending landscape and re-imported it using the technique described here. This effectively makes the landscape into a static mesh, which bypasses the landscape rendering that has the assert in it. This isn’t a perfect technique, as I lost some foliage info in the process, but for my purposes, it worked well enough.