Hi @MatsNorway1. The insctuctions mentioned that no Inventor documents can be open when you try to make edits within your Project file. However, it does not mention that no one else, nor no thing else can be referencing that Project file at that time either. For instance, many years ago all our Engineering designers using Inventor were all referencing the same, main Project file. In a case like that, the only way I could make any edits to that Project file was for everyone else to close their Inventor application (or early in the morning before they got in and started Inventor), and I had no documents open, then I would be able to make edits. We soon after created a set of duplicate Project files, so that each user had their own Project file, with their user name in the file name. Then, all I had to do was close all my own documents, and I could make changes to my Project file. Then, if needed, I could copy that one, and paste it overwriting the other Project files, making sure to preserve their unique file names, before others started Inventor in the morning. Of course that required all other users to close Inventor (and usually shut down their computers) before leaving each day. The project files, and most other 'shared' resources were located on a common server drive on our company network. I do currently, and have not in the past, used Vault, but I am pretty sure you would need to check out the Project file yourself, before you would be able to make changes to that local copy, then you would have to check it back in. And if others use the same project file, you would have to instruct those others to close all their Inventor documents, and possibly even their Inventor session, then check-out (or otherwise get a local copy of) the updated/edited project file, then make sure they have that set as the active one, before opening any documents in their new Inventor sessions.
Wesley Crihfield

(Not an Autodesk Employee)