In another thread, @artao described a problem which happened at a different stage in the process, but also produced a “Can’t open debug log” message.
According to artao, the solution was to deactivate Avast.
Don’t know if that helps, but it might be worth a try, and it’s quickly done. (Right-click the Avast icon in the system tray, then there should be an option to deactivate the protection for various periods of time, for example 1 hour. I think other anti-virus software offers similar options.)
And I guess it can’t hurt to ping @DavidK directly.