system error when writing to xml............

[Supra]

i got "system error" when saving to xml file.
i am using checkbox1 control to xml. when user clicked checkbox and set
to true and press btnOk to conform and save it to xml

rw.WriteConfigInfo("User Modes", chkInvisible.Text,
chkInvisible.Checked, "PirateChat.xml")

the error occured in hightleighted in below :.......

Public Function WriteConfigInfo(ByVal aSection As String, ByVal aKey As
String, ByVal aValue As String) As Boolean
Dim node1 As XmlNode
Dim node2 As XmlNode
If aKey = "" Then
' find the section, remove all its keys and remove
the section
node1 =
(Doc.DocumentElement).SelectSingleNode("/configuration/" & aSection)
' if no such section, return True
If node1 Is Nothing Then Return True
' remove all its children
node1.RemoveAll()
' select its parent ("configuration")
node2 =
(Doc.DocumentElement).SelectSingleNode("configurat ion")
' remove the section
node2.RemoveChild(node1)
ElseIf aValue = "" Then
' find the section of this key
node1 =
(Doc.DocumentElement).SelectSingleNode("/configuration/" & aSection)
' return if the section doesn't exist
If node1 Is Nothing Then Return True
' find the key
node2 =
(Doc.DocumentElement).SelectSingleNode("/configuration/" & aSection &
"/" & aKey)
' return true if the key doesn't exist
If node2 Is Nothing Then Return True
' remove the key
If node1.RemoveChild(node2) Is Nothing Then Return False
Else
' Both the Key and the Value are filled
' Find the key
node1 =
(Doc.DocumentElement).SelectSingleNode("/configuration/" & aSection &
"/" & aKey) <======= error occured in here.
If node1 Is Nothing Then
' The key doesn't exist: find the section
node2 =
(Doc.DocumentElement).SelectSingleNode("/configuration/" & aSection)
If node2 Is Nothing Then
' Create the section first
Dim e As Xml.XmlElement =
Doc.CreateElement(aSection)
' Add the new node at the end of the
children of ("configuration")
node2 = Doc.DocumentElement.AppendChild(e)
' return false if failure
If node2 Is Nothing Then Return False
' now create key and value
e = Doc.CreateElement(aKey)
e.InnerText = aValue
' Return False if failure
If (node2.AppendChild(e)) Is Nothing Then
Return False
Else
' Create the key and put the value
Dim e As Xml.XmlElement =
Doc.CreateElement(aKey)
e.InnerText = aValue
node2.AppendChild(e)
End If
Else
' Key exists: set its Value
node1.InnerText = aValue
End If
End If
' Save the document
Doc.Save(FileName)
End Function

regards,

[Supra]

<configuration>
-
<PirateChat>
<RealName>PirateChat XP Prof 2004 version 1.0 </RealName>
<Email>su***@toyota.com</Email>
<Nick>doremafa</Nick>
<AltNick>djanjo</AltNick>
<Pswrd>supra</Pswrd>
<Network>Undernet</Network>
<Server>eu.undernet.org</Server>
</PirateChat>
</configuration>

Supra wrote:

i got "system error" when saving to xml file.
i am using checkbox1 control to xml. when user clicked checkbox and
set to true and press btnOk to conform and save it to xml

rw.WriteConfigInfo("User Modes", chkInvisible.Text,
chkInvisible.Checked, "PirateChat.xml")

the error occured in hightleighted in below :.......

Public Function WriteConfigInfo(ByVal aSection As String, ByVal aKey
As String, ByVal aValue As String) As Boolean
Dim node1 As XmlNode
Dim node2 As XmlNode
If aKey = "" Then
' find the section, remove all its keys and remove
the section
node1 =
(Doc.DocumentElement).SelectSingleNode("/configuration/" & aSection)
' if no such section, return True
If node1 Is Nothing Then Return True
' remove all its children
node1.RemoveAll()
' select its parent ("configuration")
node2 =
(Doc.DocumentElement).SelectSingleNode("configurat ion")
' remove the section
node2.RemoveChild(node1)
ElseIf aValue = "" Then
' find the section of this key
node1 =
(Doc.DocumentElement).SelectSingleNode("/configuration/" & aSection)
' return if the section doesn't exist
If node1 Is Nothing Then Return True
' find the key
node2 =
(Doc.DocumentElement).SelectSingleNode("/configuration/" & aSection &
"/" & aKey)
' return true if the key doesn't exist
If node2 Is Nothing Then Return True
' remove the key
If node1.RemoveChild(node2) Is Nothing Then Return
False
Else
' Both the Key and the Value are filled
' Find the key
node1 =
(Doc.DocumentElement).SelectSingleNode("/configuration/" & aSection &
"/" & aKey) <======= error occured in here.
If node1 Is Nothing Then
' The key doesn't exist: find the section
node2 =
(Doc.DocumentElement).SelectSingleNode("/configuration/" & aSection)
If node2 Is Nothing Then
' Create the section first
Dim e As Xml.XmlElement =
Doc.CreateElement(aSection)
' Add the new node at the end of the
children of ("configuration")
node2 = Doc.DocumentElement.AppendChild(e)
' return false if failure
If node2 Is Nothing Then Return False
' now create key and value
e = Doc.CreateElement(aKey)
e.InnerText = aValue
' Return False if failure
If (node2.AppendChild(e)) Is Nothing Then
Return False
Else
' Create the key and put the value
Dim e As Xml.XmlElement =
Doc.CreateElement(aKey)
e.InnerText = aValue
node2.AppendChild(e)
End If
Else
' Key exists: set its Value
node1.InnerText = aValue
End If
End If
' Save the document
Doc.Save(FileName)
End Function

regards,