Mac OS Update to 10.14.5 error
The error could be the download progress was interrupted.

The macOS updated files are located in /Library/Updates, needs to clean up that folder. You can't simply delete it. 

By the following steps:


Restart your mac, press Command + R, then enter into Recovery HD.
Choose utility menu, select Terminal.
csrutil disable to disable SIP.
reboot.
Delete the files in folder /Library/Updates.
Enter Recovery HD again, and input csrutil enable in Terminal.
reboot.
Check the update should work.


Hope this helps someone.