Import failed when placing .indd file, while user has file open. (on SMB share).
User receives the message, "Import failed." when placing a .indd file inside of another InDesign file.

If this is a limit of InDesign it would be helpful if the error message was more detailed. If this error prompted the user to close the open file, it would be clear what is causing the issue. I believe that I have been able to place an open InDesign file in the past.