So, its been some time, still having an issue? That is a very specific message but I can understand it being triggered if you are trying to change the team on a non-latest iteration. You can only do that from latest iteration. You said this was new items so things that have not been checked in yet. CAD docs or WTParts? There should be a message in the MethodServer logs that would be helpful if you could post it.
Are there any listeners or customizations in play that would be trying to modify data behind the scenes as its create but before check in? Another question is this across the board for all users, all context or just sometimes? It could be something with Object Initialization Rules, maybe. Say you upload to one context but try to check in to another that has a different team setup in the OIR definition. Could that cause the behavior? @MG_10170125 , need more info on what you are seeing.