PLEASE HELP trying to get data from xml using c#

[C# Programming]

hi im doing a small project for friend.. i need to get the data out of xml so that i can verify the username and password
xml is like this

PLEASE HELP THE ERROR I GET IS EXPLAINED IN THE MIDDLE.. THANKS ALOTTTT



Password="pass"
/>

Password="pass78"
/>


and to get the value im doing

private void button1_Click(object sender, EventArgs e)
{
XmlDocument xmldoc = new XmlDocument();

xmldoc.Load("path.xml");

System.Xml.XmlNodeList client;
XmlNode clientNode = xmldoc.DocumentElement;

client = clientNode.SelectNodes("Client");

string Usernamttext = txtUsername.Text;
string passwordtext = txtpassword.Text;



foreach (XmlNode DataNode in client)
{

string userid;
string password;


************************************************************************************************
******* ERROR HERE*** now when i run it it gives me an error when it gets to the line below that """object reference not set to an instance of an object"""
*************************************************************************************************

userid = DataNode.SelectSingleNode("Username").InnerText.Trim();
password = DataNode.SelectSingleNode("password").InnerText.Trim();

if (string.Compare(Usernamttext, userid) == 0)
{
if (string.Compare(passwordtext, password) == 0)
{
break;
UserProfile UserProfileForm = new UserProfile();
UserProfileForm.usernamevalue = userid;
UserProfileForm.Show();
this.Close();

}
else
{
MessageBox.Show("Invalid Username or password");
}
}
}


}