I will take a look at it.

There are two tools in maya to help -

1. cleanup geometry - select remove nonmanifold

2. select geometry tool - select by constraint option

What is nonmanifold geometry? I have found two simple explanations that I have found useful -

Description 1
It is geometry that can't be unfolded into a flat piece. Examples are two polygons next to each other, with normals facing in opposite directions, two planes that share a single vertex but no edge, and two polygons, with the edge extruded outward from the edge that both share (basically making a "T" shape out of 3 polygons).

Description 2
Manifold models are models where the volume is well defined.
They have the following properties:

Every edge belongs to two faces.
Every vertex is surrounded by one sequence of edges and faces.
Faces only intersect eachother in common edges en vertexes.
There is a material on only one side of a face

Another way of putting it, a manifold object is a shape that you can create in real life. non-manifold objects have qualities, where you have badly defined volumes in your shape, making it impossible to recreate the model exactly that way in real life.

Try this -------------------------------------------------------

As a good example - create a 1 x 2 polygon plane, then select the middle edge and extrude it. Then try to convert it to a sub-d and see what message you get.

Now select the object and then pick cleanup and check the remove geometry non-manifold check box and apply.

The object will be split into two polygon planes along the shared edge.

I will take a look at your geometry and see what I can find.