If it's just the error with uploading the file, it's pretty easily fixed (or rather, worked around), by following the manual upgrade process. It's not uncommon at all for that upload to fail for one reason or another. Seems to happen to me about 75% of the time, and it's not really even worth figuring out why because it's so easy to do it without using the upload process.
1. Start with your upgrader jar file. Presuming your on Windows, just rename it to a .zip file.
2. Create a new directory in d:\Vontu\Protect\updates called something like "update-11.1.6".
3. Unpack the zip into that new directory.
4. Run the start_upgrade_wizard.bat file.
5. Wait for about 60 seconds or so for it to launch the upgrader.
6. Open a browser window and go to the URL: https://[enforceserver]:8300. This should bring you to the log in screen for the upgrader UI.
7. Follow the upgrader as normal.
All of this is documented in the upgrade guide, btw. Review that first, please, as I'm just going from memory with the above steps, but that should be all you need to do.
~Keith