Hi Benoit,
Most likely, the project that you're trying to copy is opened on a slave machine and is used either by TestComplete or TestExecute. That's why it's impossible to copy this file as it cannot be overwritten. To avoid showing this message, close the project on the slave machine and try again.
One more guess: if you don't use the General Events project item in your project, you can try deleting the file specified in the error message from the project on the Master machine and try again, but I'm not sure whether it will help.
For more information on the situation you faced, please refer to the Message - File writing error on remote PC help topic.
