xml的有关问题

xml的问题
提交一个XML，但提示说XML没根元素。郁闷。大家看看

XmlDocument     fsxml   =   new   XmlDocument();
XmlDeclaration   fssmxml;
fssmxml=fsxml.CreateXmlDeclaration( "1.0 ", "gb2312 ", "yes ");
fsxml.AppendChild(fssmxml);

XmlElement   sxrmxx   =fsxml.CreateElement( "SXRMXX ");
XmlNode   s   =fsxml.SelectSingleNode( "SXRMXX ");
XmlElement     login   =fsxml.CreateElement( "LOGIN ");

XmlElement   username   =fsxml.CreateElement( "USERNAME ");
username.InnerText= "103005 ";
login.AppendChild(username);

XmlElement   password   =   fsxml.CreateElement( "PASSWORD ");
password.InnerText   = "103005 ";
login.AppendChild(password);

sxrmxx.AppendChild(login);

//XmlNode   sxrmxx2   =fsxml.SelectSingleNode( "SXRMXX ");
XmlElement   operation   =fsxml.CreateElement( "OPERATION ");
operation.InnerText= "1 ";
sxrmxx.AppendChild(operation)；

XmlElement     unitinfo   =fsxml.CreateElement( "UNITINFO ");  

XmlElement     xzqh     =   fsxml.CreateElement( "XZQH ");
xzqh.InnerText= "103005 ";
unitinfo.AppendChild(xzqh);


XmlElement     dwbm   =   fsxml.CreateElement( "DWBM ");
dwbm.InnerText= "440100 ";
unitinfo.AppendChild(dwbm);
sxrmxx.AppendChild(unitinfo);//添加unitinfo

                fsxml.Save(Server.MapPath(strFileName));

[解决办法]
最后加上 fsxml.AppendChild(sxrmxx);