macOS Big Sur Installation Problem: "An error occurred when installing macOS. You can try again to complete the installation."

Hello msgames2000, 

Welcome to the Apple Support Communities! From your message we understand that you're having an issue downloading and installing the new macOS Big Sur. 

Begin by through the following troubleshooting steps on your Mac: 

1 - Quit all apps. If an app will not quit, follow these steps to force it to quit: How to force an app to quit on your Mac. 

2 - Disconnect any peripherals that you have connected to your Mac at this time. This includes any external hard drives, audio devices, or printers, etc. 

3 - Restart your Mac: Go to the Apple menu in the top left corner of your screen > Restart. 

4 - Try reinstalling the update. 

5 - If you're seeing the same results, restart in safe mode and test again: How to use safe mode on your Mac. 

6 - If still occurring in safe mode you’ll need to create a new user, sign into that new user with your information, and test it out again. This article will show you how: Set up users, guests, and groups on Mac.

All the best.