ConfigurationSection properties cannot be edited when locked

I'm trying to add URL Mappings whenever a new page is added to the database, this is the code I have, but it keeps erroring out:

                  System.Configuration.Configuration configuration = WebConfigurationManager.OpenWebConfiguration("~/Web.config");
                  UrlMappingsSection ums = (UrlMappingsSection)configuration.GetSection("system.web/urlMappings");
                  UrlMappingCollection umc = ums.UrlMappings;
                  UrlMapping um = new UrlMapping("~/" + sUrl, pageURL + "?pageID=" + pageID.ToString());            

Network Service and ASPNET both have read/write access to the file.

The error is:
Exception Details: System.InvalidOperationException: ConfigurationSection properties cannot be edited when locked.

on the configuration.Save() line
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Elvio Lujan.Net Senior DeveloperCommented:
you can't modify the web.config file this way...
you need to edit the file and save overwiting it
whityumAuthor Commented:
This code is from the microsoft site:
Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs)
   Dim myconf As Configuration = WebConfigurationManager.OpenWebConfiguration("/ASPNET20CC")
   Dim myUrls As UrlMappingsSection
   Dim myGroup As System.Web.Configuration.SystemWebSectionGroup = myconf.GetSectionGroup("system.web")
   myUrls = myGroup.UrlMappings
   myUrls.UrlMappings.Add(New UrlMapping(txtUrl.Text, txtZiel.Text))
   If Not myUrls.LockItem Then
   End If
End Sub

I converted it to C#, and even attempted to unlock the UrlMappingsSection and it still says ConfigurationSection properties cannot be edited when locked

            Configuration myconf = WebConfigurationManager.OpenWebConfiguration("~/Web.config");
            System.Web.Configuration.SystemWebSectionGroup swsg = (SystemWebSectionGroup)myconf.GetSectionGroup("system.web");
            UrlMappingsSection ums = swsg.UrlMappings;
            ums.LockItem = false;
            UrlMapping um = new UrlMapping("~/" + sUrl, pageURL + "?pageID=" + pageID.ToString());            
            ums.SectionInformation.ForceSave = true;
            return true;

Has anyone added URL Mappings in code successfully?
whityumAuthor Commented:
and lem2802, why do you say that?

there is a whole management API to edit the configuration
whityumAuthor Commented:
I changed Configuration myconf = WebConfigurationManager.OpenWebConfiguration("~/Web.config"); to

Configuration myconf = WebConfigurationManager.OpenWebConfiguration("/projectName");

and it works.
PAQed with points refunded (500)

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