problem while writing XML

i have one XML file as
<?xml version="1.0" encoding="utf-8"?>
<Preference>
<MessageSetting AutoStart="False" RUserPassword="True">
<UserID>123123</UserID>
<UserPassword>VvetqIEfbbA=</UserPassword>
<OrganizationIDList> <OrganizationID>ABC_MORTGAGE</OrganizationID>
</OrganizationIDList>
<RecentOrgID>ABC_MORTGAGE</RecentOrgID>
</MessageSetting>
<preferences>

In this file i have to add(not replce) node at organisation id ie add another organisation id in organisation list How can i do this?

I'm using nsisXML plugin
${nsisXML->CreateElement}
but its giving eroor
It'll be very helpful if some one can give me code example

Your:

<?xml version="1.0" encoding="utf-8"?>
<Preference>
<MessageSetting AutoStart="False" RUserPassword="True">
<UserID>123123</UserID>
<UserPassword>VvetqIEfbbA=</UserPassword>
<OrganizationIDList> <OrganizationID>ABC_MORTGAGE</OrganizationID>
</OrganizationIDList>
<RecentOrgID>ABC_MORTGAGE</RecentOrgID>
</MessageSetting>
<preferences>

Should:

<?xml version="1.0" encoding="utf-8"?>
<Preference>
    <MessageSetting AutoStart="False" RUserPassword="True">
        <UserID>123123</UserID>
        <UserPassword>VvetqIEfbbA=</UserPassword>
        <OrganizationIDList> 
            <OrganizationID>ABC_MORTGAGE</OrganizationID>
        </OrganizationIDList>
        <RecentOrgID>ABC_MORTGAGE</RecentOrgID>
    </MessageSetting>
</preferences>

One could try to improve the XML Plugin e.g. by stripping spaces first and ten evaluate.

Note: Valid XML not called "file" but "Document"

As Joel corrected, the OPs root element wasnt closed (not sure if this was the issue), but it cant hurt to validate the XML.

guys soory to put the wrong doc but i have checked the file & root element is closed properly in it i just need the code to add elements to <OrganizationID> (multiple elements)

<Preference>
...
</preferences>

should be either "Preference" or "preferences" in both cases...

<Preference>
</Preference>
guys i'm telling u there is no problem with XML please just tell me how can i add more than one OrganizationID's
ie
<OrganizationID>1234</OrganizationID>
<OrganizationID>5678</OrganizationID>
<OrganizationID>9012</OrganizationID>
i need code some problem with code that i wrote i'm new to both NSIS & XML

If you are using my plugin see example-2.nsi