Export always has a chunk missing

When I try to export my project enclosure from MakerBot, there is some funkiness in how it builds it. It looks fine in Sketchup and in Makerbot (before I try exporting it.)
So I tried making a super simple block in Sketchup, imported it into MakerBot, and the weirdness is still there.
Do you have any idea what might be causing this?

Screen grab of the project enclosure:
Attachment 7357

Screen grabs of a simple block:
Attachment 7358Attachment 7359