Hi Tree, yeah that's quite a large file so you're probably running out of memory and having various things fail due to that.

The easiest thing to try is to adjust the "Mesh angle" settings under Options > View as described here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=4643.2

Setting the "Mesh angle" to a rougher angle like 25 degrees and unchecking "Add detail to inflections" will make for a somewhat rougher looking display but also lighten up the density of the display meshes and that can help reduce memory consumption by quite a bit on more complex models.

If that doesn't help solve it for you, you may need to export the STEP file from where you are creating it in multiple chunks (like half the model in one piece, and half in another piece) rather than all in one single giant file.

- Michael