Installed KeePass (2.27) on PC (Win 8.1) and am using DropBox for my encrypted file. I download KeePassDroid (v. 1.99.11) on my Android. I open DropBox on my Android and navigate to my encrypted file (.kdbx). When I open this file my Android automatically opens KeePassDroid and prompts me for a "password and/or key file to access your database". I don't use a key file so I enter my password but I keep getting, "invalid password or key file". I'm using the same password to access my database from my PC and that works fine.
It works for me on Android 4.3, with Dropbox and KeePass 2.27 on Win 7 Home Premium (OS doesn't matter, neither does the KeePass version if it is reasonably recent).
Thanks. I went back to the PC, clicked File->Change Master Key, changed it to the very same password but made sure "Windows User Account" wasn't checked and now everyone is happy.
When you check the windows user account box the Windows User Account becomes part of the Master Key.
Going forward: Use the Windows User Account link with care. See the warning at http://keepass.info/help/base/keys.html#winuser