Electrical Theory: Zener Voltage Regulator

I am developing a lesson plan on zener voltage regulators. We've used one zener circuit for several decades, but it appears to lack a formal feedback network. Therefore, using multiSIM 8 software, I drafted a second zener circuit that looks like those in textbooks and online (e.g., https://www.circuitstoday.com/controlled-transistor-series-regulator). Unfortunately, despite being a common design, when I run a simulation, I encounter errors at random voltages throughout the 6-100v unregulated power supply range. I have called and emailed multiSIM's owner, National Instruments (https://www.ni.com/en-us.html); however, due to the lack of a service contract, I cannot speak to an engineer. I have also emailed the webmaster at https://www.circuitstoday.com/ and the author of https://electronicspost.com/, but neither reply. In short, I am at a loss for contacting a good-willed, competent electrical engineer to (1) assess the design of our original zener voltage regulator circuit and (2) justify why the common zener voltage regulator circuit errors during simulations based on the input voltage. Perhaps a fellow BMET here has a contact I could reach out to? I have two zener circuit and an error log file I can share with anyone willing to help. Thank you for your attention and consideration.