ICEM incapable of writing ANSYS input mesh with midside nodes
 

I have produced a fairly large structural mesh with tet and prism elements with ICEM (~5million elements). ICEM has no problem creating an input file (using file -> export -> ansys) which I can then load into ANSYS APDL.

However, the analysis is static structural and requires midside nodes. So I have added these easily in ICEM with the modify mesh -> mesh type -> add mid side nodes.

The problem comes when I try to export the mesh with the mid side nodes to ANSYS. ICEM initiates the process with the message "please wait writing input file..." but then it just stays in that condition indefinitely. It basically hangs. I have left it overnight, and even after 8 hours nothing changes.

Why is the export not functioning with the mesh with added midside nodes, while it has no problem exporting the same mesh with lower order elements?