Boot Camp - stops while creating flash disk with Windows 10

I am trying to install Windows 10 1709 on my MacMini (Macmini7,1, acquired at the end of 2015). I had Windows 10 on this MacMini before (earlier release 1694), just wanted to make fresh installation.

I reinstalled OS on MacMini (Maverick), then upgraded it to High Sierra. Then installed all updates. Everything fresh and clean from MacOS point of view.

I downloaded Windows 10 .iso file from microsoft.com.

When I try to create flash disk with Boot Camp Assistant I get error «It is not possible to set a software as up-dating is unavailable via the Software updating server» (not exact wording, I see this text in Russian - «Не удается установить ПО, так как обновление недоступно через сервер Обновления ПО.»).

I tried several times, the same error.

Could anybody give a hint?