[jcifs] Unable to identify resons for SMB Exceptions

[James]

Hello,
       I am James, i am using SMB jcifs library for one of my java
application and all works fine but some time i found weird issues when i
firing a request to remote machine(SMB server) and i don't understand the
cause of an exception most of the cases so i have noted down some points
below which get me confused.

There is no any explanation of exception that is being raised by server on
API docs, they just provides constants using NTStatus.

# I want to know the cause/reason when these exception are being raised:

1. NT_STATUS_UNSUCCESSFUL 

- As per my finding it says "A device attached to the system is not 
functioning." 

My Que: Is that means that requested device/machine(SMB server) have no
support for smb or SMB is unable to request the server ?

2. NT_STATUS_NO_LOGON_SERVERS

- As per my finding "There are currently no logon servers available to
service the logon request."

My Que: what is the reason behind this exception, is there any problem in
remote machine like system is down/slow or it's internet connection's speed
problem so that i can't connect to server.