We have just had a very similar if not the same problem,
I had imported an XREF into my file, to which I then detached at a later date, (none of the layers were removed so had to do this through Attribute Manager, - which I understand is another issue.
we then go to import the same xref (with the same name) but from a different folder and it says the same error as above, that another with the same name exists.
I had reported this to the Graphisoft helpline which they confirmed that had not heard of, so I sent them to this post.
Are there any fixes as yet? as we dont really want to have the change the xref name
JB - AC25 - Windows 10 -