Hi Peter,

> What's going wrong?

MoI is running out of memory just as the message says - MoI is a 32-bit program and so it is only able to use about 4GB of your RAM and not all of it.

If you are generating a quite large density mesh that overflows that amount you may need to export it in some separate chunks rather than trying to create one single gigantic output file all in one go.

To do that select some different pieces of your model and use File > "Export" rather than File > "Save As" - Export is short for "Export selected objects", and it will only write just the objects that are currently selected to the output file so that should help to avoid running out of 32-bit address space.

- Michael