Guys,
it was incorrect certificate. They insisted that the cert is correct and there is no other. Then they found another cert and it worked.
The error "Additional info: error:14090086:lib(20):func(144):reason(134)" means that the cert is not trusted. You can also see in the log above that the Netapp connects successfuly to DC on port 389. The initial connection is in plain text and after that it tries to upgrade to encrypted connection using the cert. And it fails if the cert is wrong.
That's it.
Jan