Error installing Big Sure

When I try to update to Big Sure i. get in. the UI the. error message that an error occurred while installing the selected update.

Current version is Catalina 10.15.7

In the system.log this entry is added:

com.apple.xpc.launchd[1] (com.apple.xpc.launchd.domain.pid.SoftwareUpdateC.1156): Failed to bootstrap path: path = /System/Library/CoreServices/Software Update.app/Contents/Resources/SoftwareUpdateConfigData, error = 2: No such file or directory

The file SoftwareUpdateConfigData is present.

Any advice to solve the issue?

Regards, Rob