Windows 10 anniversary update fails with 0x80070057 error.

Go to Windows Update, by opening the start menu, search for 'update' and open "Check for Updates". Now look down for Learn More and click on it, it should open a link on your default browser, now click on 'Get the Anniversary Update now'. File name should be 'Windows10Upgrade28084'.  

Open it and make sure it downloads the files. Watch for Verifying Download and make sure to turn off your Internet/WIFI/LAN if it reaches 100% IMMEDIATELY. since you already have the error, file is already on your computer so it's going to just verify like a hash check to make sure the Windows 10 update files are intact.

Now it should install upgrades but get stuck at the usual 2%, make it stay there for about 30 seconds and re-enable your Internet/WIFI/LAN and the upgrade should finally pass 2%. You can then live in peace.

By golly, disabling then re-enabling the network did the trick!  Thank you, TheCFCHenri!!

I had already downloaded the file with several previous attempts, and so I started the process, let it verify the download, disabled all network adapters, waiting for a couple minutes when it appeared to hang at 2%... then re-enabled adapters, and after about 30 seconds it started to proceed.  Much appreciated!

Thank you for reporting this issue.  With your help, we were able to fix the issue that was causing error code 0x80070057 for customers with the Windows 10 Anniversary update.  If you were experiencing this issue, please re-run the upgrade from your desktop shortcut (Windows10UpgraderApp.exe).  If you don't have the shortcut, try updating again by going to the Software Download Page and clicking Update Now.

Paul...