...
Now you have two windows where pressing the Return key directly causes an action
Press the Return key on the Reset-Page and immediately Alt-Tab to the update tool window and press the Return button again, this must be as fast as possible (Return-AltTab-Return)
In most cases this will fail, but every now and then it works.
With a little bit of luck, the installer fixes the folder, resolving the problem
If the error is still there, just use the back button on the updater page, no need to re-upload the firmware, then try the same steps again
The Reset action takes a little longer when performed the first time
Usually, when done fast, this works with less than 10 attempts
...