As of Summer 2018, SimUText is no longer qualified to run on the Mac OS X 10.9 (or lower) operating system. You will either need to upgrade the operating system on your computer or use a different computer for your SimUText assignments.
If you would like to upgrade the operating system on your computer, first check your software and printers for compatibility!! The following page on the Apple website has information on upgrading (at no cost): http://www.apple.com/macos/how-to-upgrade/
Otherwise, you will need to find another computer to complete your SimUText assignments. Your professor might have SimUText installed on some university computers. If so, you can launch the application, log in, and work on your assignments.
If you have access to a computer onto which you can install the SimUText software, you can download and install SimUText as often as you need. Sign into the Student Portal, click on the Download SimUText Installer button, and install the software from there.
If you're using a computer onto which you are not allowed to install any programs (e.g. a computer lab computer), then you might want to use our USB version of SimUText. Please refer to the article I need to install SimUText on a USB drive (Flash drive).