I get this error when trying to partition via boot camp assistant: The installer disc could not be found. Insert your Windows installer disc and wait a few seconds for the disc to be recognised. I'm using an external USB drive because my Macbook Air doesn't have an optical drive. So I put the ISO on the USB using the Microsoft Windows 7 USB/DVD Download Tool and also tried using command prompt on a Windows 7 computer to no avail. I have tried different USB drives multiple times but I still can't get it to work! I'm running Lion. I've tried to create a partition via Disk Utility but when I boot into the USB it says the partition can't be used for Windows 7 regardless of how many times I format or delete it. Any help?