If you get this error message, don't worry. Just click the OK button and you're done. Restart your Mac while holding down the Option key to go to the boot loader. Choose the EFI Boot, USB disk option. This is your Mountain Lion boot disk and it will provide you with the same tools and utilities you find when you boot to a Mountain Lion recovery partition.
Clicking the Edit button launches an Apple Script editor. If you're fluent in Apple Script, you might be able to make the error message go away or you might not. Regardless, the thumb drive you just burned, booted to, and tested works just fine, so don't sweat the small stuff.