Hi Peter, is it possible for you to send the file to me somehow so I can test with it?

Just file size alone is not a full indicator of complexity - for example if the file contains a large number of instanced repeated objects, those will expand into totally separate objects when you open it in MoI and so the actual data being handled could actually be many times 24MB.

Or it could be possible that there is some problem with the STEP import resulting in some kind of slightly mangled object which then causes a sort of "run-away" excessively dense mesh being created as a side effect from that.

It's hard for me to know for sure without being able to test it myself.

That file may be too big to send to me by e-mail, is it possible to use a file sharing service and then send the link to me at moi@moi3d.com ?

Another issue may actually be your 6-core machine - when generating meshes MoI does make use of multiple cores and that does have a side effect of consuming more memory at once as well. It is possible to limit the number of cores being used, to do that go to Options > General and push the "Edit .ini file" button. In the text file that comes up, go to the [Mesh Export] section and find the setting for ThreadLimit= and put in ThreadLimit=1 and see if that makes any difference or not.

Thanks,
- Michael