Hi glennr95306524,
Sorry that you're getting an error message "Could not use the ellipse tool because of a program error" while using Photoshop CC 2018.
Just FYI, Photoshop CC 20.0 (2019) is out now, I'd recommend that you install the latest version before troubleshooting this issue. See Keep Adobe Photoshop up to date
If not so, to troubleshoot the issue: I'd recommend that you restore Photoshop preferences to default:
Press and hold Alt+Control+Shift (Windows) or Option+Command+Shift (Mac OS) as you start Photoshop. You are prompted to delete the current settings. The new preferences files are created the next time you start Photoshop.
Note: Using the keyboard shortcut, preference files for custom shortcuts, workspaces, and color settings will also be reset to default.
(Source: Preferences in Photoshop )
Thanks,
Akash