So did you work out if your SQL Agent service account has rights?

To find the agent account, start services.MSC, go find the SQL Agent service, open it and check the...

'there is no any listing of 'backup' command or 'restore' command and its parameters.so how can i get all the available commands in sqlcmd.'

BACKUP and RESTORE commands are T-SQL commands....

To get the list of command line switchs for sqlcmd, do what you do for every other command line tool - type this at a command prompt:

SQLCMD /?

As for the...

That would indicate that the server A and B are not on the same domain.

Perhaps something in your requirements precluded this method but how about this:

DECLARE @var varchar(8000)

SET @var = ''

SELECT @var = @var + FieldName + '/'

FROM Table

SELECT @Var

There's always this old chestnut:

http://www.sqldev.net/xp/xpsmtp.htm