Did you use the wizard to make the button, or are you using the API approach?
If you are making a button which will also Copy the Parent project record, then you need to specify a text data entry field such as Project Name so that the new Project record = can be created with a name lkke Copy OfProject xyz.
But I thought you were trying to make a button which would import Tasks from a given template Project. In that case, the CopyFID is not required.