gridfs connection problem to mongo slave instance in replica set

[gerasimhovhannisyan]

Hi all
We have problem with connection to mongo slave instances. It shows
Authentication Required
2015/09/02 11:12:29 [error] 27321#0: Authentication Required
2015/09/02 11:12:29 [error] 27316#0: Authentication Required
2015/09/02 11:12:29 [error] 27313#0: Authentication Required
2015/09/02 11:12:30 [alert] 27299#0: worker process 27323 exited with fatal code 2 and cannot be respawned
2015/09/02 11:12:30 [alert] 27299#0: worker process 27305 exited with fatal code 2 and cannot be respawned

With master instance the connection is ok.
nginx version 1.8
server os ubuntu 14.04 LTS
checked with mongo 2.6 and 3.0 versions
nginx-gridfs version 0.8