Thank you, I can now reproduce this. The problem is that the "-" in the username is transformed into a "+" somewhere along the line so ModelCenter fails to find the SystemModeler kernel that it starts. I'll make sure that this is fixed for the next release.

In the mean time, short of changing your username which I assume you don't want to do (I know I wouldn't) you could perhaps use a script to start SystemModeler, something like this:

#! /bin/bash
/Applications/SystemModeler.app/Contents/MacOS/WSMKernelX +d=interactiveCorba &
/Applications/SystemModeler.app/Contents/MacOS/ModelCenter &

I also work with Sierra and a mac PRO

I had a very similar bug, but for me it happened that WSM put a wrong file name in the temporary folder. When I manually enter to this directory and rename it, I can activate WSM, but it should be soon enough afterwards.

The answer I got from the tech support was far from being satisfactory in this case. They came for file permissions or installation by and admin etc. Nothing worked but this simple "trick".

In addition, versions 4.2 and 4.1 work with no problem at all.

I think the most likely cause for that is that the SystemModeler kernel fails to start. Have you never been able to start SystemModler successfully or is this something that only recently started to fail?

What version of OS X/macOS are you running?

You could try to start the kernel manually by running the following in a terminal (adapt the path to your installation directory):

/Applications/SystemModeler.app/Contents/MacOS/WSMKernelX +d=interactiveCorba

If everything is working you should get something like

Using the Challenger kernel!!!
Created server
Dumped Corba IOR in file: /var/fol9lm3rn25s_bht528grdm740000gp/T/wsm.username.objid.SystemModeler.4.3.0
Started the Corba ORB thread with id: 0x7000002a0000