My first experience with the Windows 10 media creation tool was, in a word, terrible. After 20 minutes or so of downloading, the tool told me that “Something happened” and the only option was to exit. That’s probably what passes for error diagnostics at Microsoft nowadays. Don’t overburden the user with information in case it might be helpful, at most tell them to try again because errors magically fix themselves (and if not, they’re SOL anyway).
After applying some common sense, I guessed that the tool was probably running out of disk space and made more room on the system drive. Lo and behold, the media creation tool worked and spat out a functioning ISO image!
It should be noted that the target for the ISO image was a drive with tons of free space, but drive C: only had about 3GB free. The tool seems to need roughly twice the size of the final ISO image on the system drive before the image ends up on the target filesystem.
In the bad old days of dark 1980s, it was considered standard practice to check available disk space and if it ran out, report that that’s what happened. Apparently the old generation of programmers at Microsoft died out and the new one hasn’t learned this advanced technique yet.