I had same problem with Android 5.0.2, after copying it via Windows Explorer to a new folder (created with Windows) at the SD-card or internal memory.
I also tried to create the folder with an explorer App at the phone - but that folder I could not see at the Windows Explorer.
Afterwards I created a keepass file wit the droid-app within the same folder, and opened and closed it without any modification.
I retried to open the file from PC with the droid-app by typing in its name - now it was possible.
I have no idea why - but now it's working.