Scrivener, like many shareware programs, is distributed on a "disk image"; when you download Scrivener, the file that actually downloads is entitled "Scrivener.dmg" (or "Scrivener-Legacy.dmg", for older machines). The "dmg" stands for "Disk iMaGe". A disk image is essentially a virtual disk (and you can create your own disk images of anything for archiving purposes using OS X's Disk Utility). It is important to understand that the Scrivener.dmg disk image is intended only for installation - once you have installed Scrivener properly you can safely discard the Scrivener.dmg file. (Full instructions for installing Scrivener properly.)
Note that if you do not install Scrivener properly and instead run it directly from the disk image, when updates become available you may encounter the following error when trying to update:
This error, as explained in the message itself, indicates one of two problems: either you are running the application from a disk images so it cannot overwrite the application with the new update (because disk images are read-only), or you do not have the necessary permissions on your machine to install software. Therefore if you encounter this error, it is very likely that you have not installed Scrivener properly (you may, for instance, have dragged Scrivener from off the disk image's corkboard window and directly to the Dock, missing the important intermediary step of first placing it in the Applications folder and only dragging the copy in the Applications folder to the Dock).
To resolve the issue, it is recommended that you first uninstall Scrivener and then follow the detailed instructions on installing correctly. In newer versions of the software, it will attempt to detect when you are running it from an improper location, and give you options for rectifying the situation automatically or to cancel and install by hand.
If this does not resolve the issue and you have definitely installed Scrivener properly, check that you have the necessary permissions to install software on your machine (you must have administrator permissions to install software on OS X). If you still have problems, of course, contact us.