Hello @elisabethstrawberry,
Looks like the configuration files got damaged.
Ctrl+Alt+Del is the recommended method when an app stop responding, you can force quit the app by selecting the Task Manager option, unless the PC also stopped responding.
Whenever you need to force restart/stop the PC it's recommended to check the disks for errors,
Try run the disk repair utility to make sure there is no error on the disk: Open Terminal (admin), then run chkdsk C: /f/v, then restart Windows.
Optional: Once the disk repair is completed, run the sfc /scannow in Terminal (admin) to fix Windows installation errors.
*You can find more info about those commands by Googling them.
Try open S4TI to see if the error is gone. If it's still not working, try the following options:
Option 1 (workaround)
Try both Sims 4 Tray Importer (S4TI) and Sims 4 Tray Importer (S4TI) - 64 bits, they use separate configuration files, so one may work but won't fix the issue.
Option 2
Open the folder where S4TI was installed. default C:\Program Files (x86)\TeameeVo\Sims 4 Tray Importer (S4TI) or C:\Program Files\TeameeVo\Sims 4 Tray Importer (S4TI)
Find both s4ti-reset.bat and s4ti_x64-reset.bat then double click on each to launch the auto repair.
Launch S4TI to see if the repair worked.
Option 3
Open File Explorer then open C:\users\[yournamehere]\AppData\Local\TeameeVo or %userprofile%\AppData\Local\TeameeVo or %localappdata%\TeameeVo
Delete any folders starting with s4ti.exe_Url_ or s4ti_x64,exe_Url_.
Launch S4TI to confirm that it's now working.
Good Luck!