Issue: Error code 0x80240029 while updating Windows defender in Vista

Resolution:

Disable Windows updates.
1. Click Pearl button (Start)->Control Panel.
2. Doubel click windows update.
4. Click Turn off Windows updates.
Unchecked the box to get updates from Microsoft for other products.
5. Click Ok.

Now update windows defender. This should solve the issue.
After the update is done, enable automatic updates.