Do you have access to a Windows 8.1 or Windows 10 PC? This package seems to run more stably in those environments.
As for this particular error, I have found that the DISM tool completes the commit portion of the operation successfully (and then times out). If you are doing the DISM commands manually and you see this error, you can use command
dism /unmount-wim /mountdir:mount /discard
to complete the unmount.
Since I had so many issues with the USB 3.0 Creator tool, I decided to run the DISM commands manually. I created the attached script file, which includes all of the commands than need to be run. DO NOT ATTEMPT TO RUN THIS SCRIPT! You want to print out this file and then manually enter and run these commands. Whenever the unmount operation fails, simply use the command I showed above to complete the unmount.
Hope this helps,
USB3WIMUpdate.txt.zip 764 bytes