I tried to mount a SMB share from a synology disk station, which uses LDAP for account storage. It failed:
$ smbclient -u cweiske \\\\server\\sharename Enter cweiske's password: Domain=[SOME] OS=[Unix] Server=[Samba 4.1.18] tree connect failed: NT_STATUS_ACCESS_DENIED
It began to work when I edited /etc/samba/smb.conf:
[global] client plaintext auth = yes client lanman auth = yes client ntlmv2 auth = no
But I wanted this in my /etc/fstab, too. Unfortunately mount.cifs does not read smb.conf, but you can set the options via its proc configuration:
$ echo 0x00030 > /proc/fs/cifs/SecurityFlags $ mount /path/to/mount .. works
See the Kernel CIFS filesystem documentation.
I put the echo command into /etc/rc.local so that it gets auto-applied after reboots.