I am Len's coworker on this, and this happened to me.
It is incredibly frustrating that when copying over a large assembly, this is an entire plant, that something so simple can just stop and the whole process with no way to save the settings I had, no choice but to start all over again.
No option to ignore, no option to fix or edit, no option to go back, save settings, such a huge waste of time and zero confidence that if I try again, it's not just going to do the same thing again.
I also have run into the error of "this will create a duplicate file" or something like that, but it won't tell you which file it's related to. There are 2394 files in this assembly, how on earth am I going to determine which one is the problem?
It took me close to an hour with to get everything changed over to copy, then this silly error, and I need to spend probably another 45 min doing it again to maybe have it do the same thing.
It's also so frustrating that you can't select a whole group of items, and just change them to copy, you have to click on each and every one, it's very tedious, very time consuming, and likely to cause you to miss something.
I really like and am very impressed with Inventor as a whole, and Vault in general I have no issues with either, it's a bit quirky, but it's no problem once you get used to it, but this Copy design thing really needs improvement!
The irony is, the bigger the assembly, the more important this is, and the more likely it is to error and make you do it all over again. I would be fine with some weird quirky things to deal with, but just crapping out with no option to fix leaving you high and dry and wasting an hour or 2 or three with zero idea how to solve the issue or go back in pretty unacceptable.