We have replicated this symptom by installing the latest version of SimUText for Windows and then immediately launching the install package (the downloadable .msi file) again. Windows interprets this as an attempt to fix a problem with, or change the configuration of, an installed application.
If you encounter the Modify/Repair/Remove dialog, simply click Cancel instead of picking one of the three option buttons, and then read the message in the dialog box. It should indicate that the application was unchanged. Click Finish to close the dialog, and try launching the application from your desktop or from the Start menu group. If you are able to open the login screen and then enter your email and student-account password, you have correctly installed the application already.
If you have any problems launching the application or logging on, we recommend you simply use the Uninstall command to remove the application and then reinstall it from the downloaded .msi file.