Bootcamp Windows USB Installation Errors
The (fixed) Pre-Installation Environment (boot.wim) of your Windows_7.iso doesn't contain the necessary drivers to use the USB3-interface of your Early 2013 Macbook Retina.

To circumvent limitations (new drivers, new hardware) Microsoft uses the $WinPEDriver$-feature to provide drivers at installation time.

Apple Boot Camp uses this method to provide the necessary drivers with the boot medium - your thumb drive.

Usually the Boot Camp Assistant does the whole work properly:


Partition your drive
Download the appropriate Boot Camp Support Software
Create the Windows 7 install thumb drive (with all necessary drivers)


Please check if you meet the following requirements:


Backup of your entire hard disc
Windows 7.iso Home Premium x64, Professional x64, or Ultimate x64
(these three are us-en digitalriver isos and here is a full list of all images available there) 
Formatting of the USB-device (according to Apple):

If the size of the thumb drive is 32 GB or less it should be MS-DOS (FAT).

If the size of the thumb drive is over 32 GB it should be ExFAT.
Boot Camp Support Software version: 5.1.5621

download link: Latest Boot Camp Support Software
File/Folder structure of the root of your boot device (your thumb drive):





If your boot device doesn't contain $WinPEDriver$, AutoUnattend.xml and BootCamp please download and extract BootCamp5.1.5621.zip and copy the contents of the resulting BootCamp folder to the root level of your install drive.
If your install drive already contains those files and folders then check if the USB drivers are present.
(Paths: /$WinPEDriver$/IntelxHCISetup/Drivers/HCSwitch/Win7/x64/ and /$WinPEDriver$/IntelxHCISetup/Drivers/xHCI/Win7/x64/).
If they aren't present the wrong Boot Camp Support Software package has been chosen. Delete $WinPEDriver$, AutoUnattend.xml and BootCamp and continue with step 6.


Now the installation should work.