Hi Steve Brenia,
Since running the app as administrator produces the same error, I would avoid changing folder permissions for now. The installation itself may not have completed correctly.
Please try the following:
- Run Microsoft’s Program Install and Uninstall troubleshooter. It can repair corrupted installation/uninstall information that prevents a desktop program from being removed.
- Once Stellarium is successfully removed, restart the PC and download a fresh installer from the developer’s official site rather than reusing the existing installer.
- If a fresh installation still will not open, test it after performing a clean boot. If the app works there, another startup application or service is likely interfering with it.
If the troubleshooter cannot remove Stellarium, please let us know what error it reports. That should help narrow down the next step without making unnecessary system changes.