If you’re trying to connect via SCP or SFTP, a the server mumbles errors about looking user groups and unexpected directory listing commands, you’re probably connecting to a Drobpear.
The thing is, Dropbear is designed to have minimal resource footprint, and even if you disable group check, the directory listing error still remains, since Dropbear doesn’t support file transfer.
To exchange files, install OpenSSH, SSHDroid or any other server with SCP and SFTP support.