dump database命令请教

资料上说备份数据库的语法为：  dump database database_name to dump_device
例如：dump database mydb to mydb-bk

我试图通过如下命令备份master数据库提示错误
use master
dump database master to 'd:\mydata\master20081120.dat'
go
------------------------ Execute ------------------------
WARNING: In order to LOAD the master database, the SQL Server must run in single-user mode.  If the master database dump uses multiple volumes, you must execute sp_volchanged on another SQL Server at LOAD time in order to signal volume changes.
Can't open a connection to site 'SYB_BACKUP'.  See the error log file in the SQL Server boot directory.
Can't open a connection to site 'SYB_BACKUP'.  See the error log file in the SQL Server boot directory.
----------------- Done ( 2 errors ) ------------------

通过如下命令备份model数据库提示错误
use model
dump database model to 'd:\mydata\model20081120.dat'
go
------------------------ Execute ------------------------
Can't open a connection to site 'SYB_BACKUP'.  See the error log file in the SQL Server boot directory.
Can't open a connection to site 'SYB_BACKUP'.  See the error log file in the SQL Server boot directory.
----------------- Done ( 2 errors ) ------------------

出什么错是知道了，但不知道怎么处理!
1:如何让sql server运行在单用户模式？
2:dump_device是个什么样的概念，简单说是一个路径（象我写的那样）还是需要预先定义？
3: Can't open a connection to site 'SYB_BACKUP'. 一般是什么原因，我在sql server根目录下的log文件中没有发现有用的信息啊？

谢谢（初次弄这个，烦大家多多帮助）！

备份服务没有起

确认一下远程服务器中有没有这样一个syb_backup的服务,印象中12.5.X一个版本中要手动去配