Prohibitory Sign-Cannot fresh install OS X from USB

Hello all,

I am needing some guidance for a fresh install on a Mac Book Pro. This Mac came with OS X 10.11.2 on it and I need to downgrade to a previous version due to security software that does not work at this system level yet. I need to get to 10.11.1. Current things tried.

- Tried to downgrade just by installing the 10.11.1 package but as I figured NO GO.

- Deleted current OS and used "Reinstall OS X" function but it only goes to the internet and gets the most up to date version.

- Tried reinstalling OS X 10.11 by downloading and creating a USB drive to boot from. I'm pretty sure this is the best approach!!

So here is my issue, I have created a USB boot installer for OS X 10.11 El Capitan. I have gone into disc utility and erased and formatted the partition used for the previous install. I then reboot into installer mode (Hold Option), I then select the USB drive and the installer starts up but about halfway through the installation progress bar the mac all of the sudden throws a prohibitory symbol. I really need to get this process resolved so any help would be appreciated!!