It's peculiar that a reinstall didn't fix that.
First try correctly setting the catalog using the following command in Terminal (the whole thing, including the text that appears as a link):
sudo softwareupdate --set-catalog https://swscan.apple.com/content/catalogs/others/index-10.11seed-10.11-10.10-10.9-mountainlion-lion-snowleopard-leopard.merged-1.sucatalog.gz
Also, have you tried booting into Safe Mode, or booting normally but creating a new temporary admin account and updating from there?
Follow these steps to start up into safe mode.
- Start or restart your Mac.
- Immediately after you hear the startup sound, press and hold the Shift key.
- Release the Shift key when you see the Apple logo appear on the screen.
After the Apple logo appears, it might take longer than usual to reach the login screen or your desktop. This is because your Mac performs a directory check of your startup disk as part of safe mode.
If you're not sure if your Mac is started in safe mode, you can use System Information to check this. The Software section of the System Information lists the Boot Mode as "Safe" instead of "Normal" when you're started in safe mode.
Thank you @GABolz910 - worked for me