I tried many different option to access a list in Central Administration from a web part in my application. Of course the problem is that the application pool account cannot access the list and there are many variations of access denied that I found on my way….
// Get the Url for Central admin
SPAdministrationWebApplication caWebApp = Microsoft.SharePoint.Administration.SPAdministrationWebApplication.Local;
// open the list Service
Lists listService = new Lists();
listService.Url = caWebApp.Sites.RootWeb.Url + “/_vti_bin/Lists.asmx”;
// Set the credentials to use
listService.UseDefaultCredentials = true;
listService.PreAuthenticate = true;
Hopefully this will help someone else one day.