SOLUTION
Do you have any other applications open that are possibly accessing the optical drive that your disk is in?
I bet you have.
In my case I was watching a DVD using Classic Media Player but I also had open Windows Explorer which was accessing the optical drive to show me files.
After closing both applications and clicking on "Try Again", the installation
continued and loaded fine. After starting I was able to resume the other applications and use them as normal.
So click on "Try Again" or by re-running the setup.exe (or autostart.exe) from the disk.
Hope this helped you as it had me confused for an hour.
