system error when writitng 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.WriteConfigI nfo("User Modes", chkInvisible.Te xt,
chkInvisible.Ch ecked, "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.DocumentEl ement).SelectSi ngleNode("/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.DocumentEl ement).SelectSi ngleNode("confi guration")
' remove the section
node2.RemoveChi ld(node1)
ElseIf aValue = "" Then
' find the section of this key
node1 =
(Doc.DocumentEl ement).SelectSi ngleNode("/configuration/" & aSection)
' return if the section doesn't exist
If node1 Is Nothing Then Return True
' find the key
node2 =
(Doc.DocumentEl ement).SelectSi ngleNode("/configuration/" & aSection &
"/" & aKey)
' return true if the key doesn't exist
If node2 Is Nothing Then Return True
' remove the key
If node1.RemoveChi ld(node2) Is Nothing Then Return False
Else
' Both the Key and the Value are filled
' Find the key
node1 =
(Doc.DocumentEl ement).SelectSi ngleNode("/configuration/" & aSection &
"/" & aKey) <======= error occured in here.
If node1 Is Nothing Then
' The key doesn't exist: find the section
node2 =
(Doc.DocumentEl ement).SelectSi ngleNode("/configuration/" & aSection)
If node2 Is Nothing Then
' Create the section first
Dim e As Xml.XmlElement =
Doc.CreateEleme nt(aSection)
' Add the new node at the end of the
children of ("configuration ")
node2 = Doc.DocumentEle ment.AppendChil d(e)
' return false if failure
If node2 Is Nothing Then Return False
' now create key and value
e = Doc.CreateEleme nt(aKey)
e.InnerText = aValue
' Return False if failure
If (node2.AppendCh ild(e)) Is Nothing Then
Return False
Else
' Create the key and put the value
Dim e As Xml.XmlElement =
Doc.CreateEleme nt(aKey)
e.InnerText = aValue
node2.AppendChi ld(e)
End If
Else
' Key exists: set its Value
node1.InnerText = aValue
End If
End If
' Save the document
Doc.Save(FileNa me)
End Function


my output look like this:
<configuratio n>
-
<PirateChat>
<RealName>Pirat eChat XP Prof 2004 version 1.0 </RealName>
<Email>su***@to yota.com</Email>
<Nick>doremaf a</Nick>
<AltNick>djanjo </AltNick>
<Pswrd>supra</Pswrd>
<Network>Undern et</Network>
<Server>eu.unde rnet.org</Server>
</PirateChat>
</configuration>

regards,