I copy my windows project to dropbox. But scrivener is not able to open it.
I have Yosemite, last versions on PC and MAC of scrivener. The message is looking for a « binder.scrivproj file. No file are visible from mac, only rtf. They are visible in dropbox from my PC. no file named binder.scrivpro, only project.scriv exists and not visible in mac.
Did you, perhaps, copy only the content of your Windows project folder to the Mac?
The document structure of Scrivener is cross-compatible, but it requires that you sync the folder containing your project as a whole, not just its contents. You may find this article useful.
Hope this helps!