The animation looks fine in 3D view, but I can't export it to AVI. The screen is blank whenever I try to export it to AVI.
From your screenshot it looks like the 3D window is hidden behind other windows in the preview. The order of the enabled windows in the list (in the upper right corner of the Content tab) determines the back to front precedence of window in the preview. Your 3D window is at the bottom of the list, meaning it's behind all the other windows. Select "3D Using dates[Best]" and use the up arrow to move it above the Timeline and Gantt. You may also need to resize the 3D view in the preview once you've moved it forward.