Mesh.validate did the trick. Thank you Philipp for your help.

You can also change to flat shading. Thus:

The crash is related to Auto Smooth. If I disable it I can enter edit mode without problems. All polygons in the mesh are set to smooth by the import script.

Somebody pointed out that applying the multires modifier implicitly moves it to the top of the stack. If you apply the armature modifier first and then the multires, the problem persists. In the dense mesh, the offending vertices are 204528 and 208935. The location of the first vertex and its nearest neighbors (those selected in picture below) are

The stray vertices snap back into position once the multires modifier is applied.

I think I have another instance of the same bug. Look at the vertex behind the last tooth at resolution 0, 1, and 2. Unfortunately the mesh is as heavy as before.

With some extra work I did manage too squeeze everything into 256 characters. The worst case is the following expression that weighs in at 190+.

It is the first string that contains more than 256 characters. The expression is put in an ordinary string before assigning it to the driver, in order to generate a better error message.

I uploaded a very rough Autocad importer to rapidshare four years ago, It was very incomplete and never had any official status, and I have forgotten everything about it. If anybody has made any official release it must be migius, whose has spent quite a while on his importer.. He can be found on blenderartists.