I have experienced a very annoying error, has taken half my production time and made me lose information.
Most of times I have to close the CAD via task manager, because crashes completely.
Check the attached image that shows the message.
It is as if another user is modifying the project files, but no one else is connected. Sometimes it appears that myself is blocking myself.
Have you check to see if there is a project.xml.lock file in the same folder as your project.xml (project folder)? You should be able to delete it, if you are out of Plant.