Access denied to Private Shares via LDAP(CIFS: Authentication for user [DOMAIN\userlogin] has FAILED)

Hello, Community.

We installed NAS WD My Cloud EX2 Ultra (Firmware Version: 2.30.174) in the network with Windows Active Directory.
Also we have configured LDAP integration - Active Directory is ON and configured successfully.
Windows Services with Max SMB Protocol - SMB2.
Network Clients is Windows7/8/2008/2012.
But, when we create private SMB share and setup access rights for some users in the User Access list – NAS recognizes login, but refuses to authenticate user and we get following message in the log file:

Logs: CIFS: Authentication for user [DOMAIN\userlogin] has FAILED

This issue occurs with every private shared folder.

We need private shares to work correctly – this is mandatory requirement for NAS.

How can we solve this issue?
Maybe there is some firmware upgrade to fix this bug?

There are number of posts on the WD Community portal about this issue, but no solution so far.
Please help.

Thank you beforehand.

Thank you, All.

Problem is SOLVED.

Resolution: If User grand Read/Write (or Read) access to Private folder, but his default security group does not have any access to this folder - system reply DENY.
Detailed description look at:

Important: When need to grant access to the some folder for user, your need grand access to the same folder his default security group in AD obligatorily!

P.S. Is the little stupid, but why not…