Hi beanworks - that means that some edges in there did not get joined together.

You can see which particular ones are still open by setting up a shortcut key with this script on it:

script: /*Select naked edges*/ var gd = moi.geometryDatabase; gd.deselectAll(); var breps = gd.getObjects().getBreps(); for ( var i = 0; i < breps.length; ++i ) breps.item(i).getNakedEdges().setProperty( 'selected', true );

That's convenient to put on the N key so that when you push N the "naked edges" in the model will highlight - those are the edges that are not joined between 2 different surfaces, and those are the openings that you need to resolve in order to make the object a full solid.

To set up the shortcut key, go to Options> Shortcut keys and push the Add button to add in a new one at the top. For the key part (the left-hand column) put in N and then for the right side command column copy the above script and paste it in.

Then you can push N to see the unjoined edges in your model.

There's maybe some little gap in there or possibly one of the edges that was messed up and causing the problem there before was still in the model since when you deleted one face, the trimming boundary edge that the face shared with the adjacent ones is still there.

It's going to be pretty difficult to help you as well as I could if you could send me the model - is it possible for you to send it to me privately at moi@moi3d.com through e-mail instead of posting it here?

Otherwise, you may need to do some kind of object repair work which is somewhat advanced stuff. There is a tutorial available here that goes over the techniques involved of untrimming and retrimming surfaces though:
http://moi3d.com/forum/index.php?webtag=MOI&msg=446.17

- Michael