I recently began experiencing the same problem with my Galaxy SIII after upgrading to Android 4.3. Unmounting the SD card, installing the app, then remounting the SD card works, but is not a "solution" I was happy with. I finally arrived at a solution that may work for other phones, as well.
First, I created a new folder on my laptop, then copied all of the folders and files from my SD card to that new folder. I then unconnected the phone from laptop and reformatted the SD card (yes, it will delete all files and folders on the card, but that is the idea). After reformatting, I copied all the files and folders back to the phone from the laptop. Went to Play.Google and tried installing several apps that had previously been giving me the error message and - NO MORE ERROR MESSAGE!!
Apparently the SD card needs to be formatted with Android 4.3 OS to work as it should - older OS leads to an incompatibility issue.