SQL installation fails towards the end of installation (when it attempts to start the database service) with an "Access Denied" error message. While this sounds like a user permissions error, it was actually a group policy error.
1. Click Start >> Run >> gpedit.msc
2. Drill down to Computer Configuration > Windows Settings > Security Settings > Local Policies > User Rights Assignment
3. Find Debug programs in the list
4. Add the service account that will be running MSSQL
5. Reboot the machine and re-install SQL.
Group Policy Object