Things that have worked for me in the past.
Reboot the PC and let it settle down (i.e., get to desktop, let it finish autoloading whatever is on startup etc)
Disable A/V and Firewall, Anti-Spyware etc.
Try the d/l again
If it fails, exit out and restart the sim again.
If it’s still failing, watch the d/l carefully, make note of which file it’s bouncing on and then stop the sim.
Go to that file and manually delete it.
Restart sim.
I know it’s a lot, but that’s what worked for me before.