I spent a whole day wracking my brains out and eventually figured it out.
It can install the wrong driver automatically so you need to go to Device Manager>Monitors. Double click the monitor. If it installed incorrectly, it will be listed as Standard pnp-monitor. Double click it and go to Update driver and click Browse for driver software on your computer then select Let me pick from a list of device drivers on my computer. There should be two drivers in here one that is pnp Monitor Standard and one that is Generic Pnp Monitor; you need to select Generic pnp monitor driver then complete the wizard.
I didn't even need to restart, the screen split software just kicked straight in once I did this.