samba - Mar 2013 - DCERPC_FAULT_ACCESS_DENIED what is wrong?

Hello,

what is the cause of this error?

[2013/03/21 15:22:41,  1] 
rpc_client/cli_pipe.c:949(cli_pipe_validate_current_pdu)
   cli_pipe_validate_current_pdu: RPC fault code 
DCERPC_FAULT_ACCESS_DENIED received from host xxx.yyy.zzz!

Thanks,

Ricardo