Error in REST https call to get the Auth token

Hi All,

I am using F5 14.1.5.6 version of F5 and trying to get auth token from 

/mgmt/shared/authn/login

But getting 401 error, please find the detailed error message. Can any one help me with this issue.

[{"code":401,"message":"Unable to process request /tm/auth/source. Service is unavailable.","referer":"10.3.4.112","restOperationId":343185765,"kind":":resterrorresponse"}]