Try to use Samba on Ubuntu in the VirtulBox, access from Windows always failed,
Check the Samba log:
Result as below (partially copy),
../source3/lib/util.c:801(smb_panic_s3) smb_panic(): calling panic action
This command resolved the problem,
$ apt-get install --reinstall libsmbclient libsmbclient-dev libtevent0 libtalloc2
It seems that the new samba package poorly specified the dependencies it needed, so require to re-install these library.