Authentication - Can Use SharpSVN In C#

Trying to use use SharpSVN in an ASP.NET app. So far, it's been nothing but trouble. First, I kept getting permission errors on "lock" files (that don't exist), even though NETWORK SERVICE has full permissions on the directories. Finally in frustration I just granted Everyone full control. Now I get a new error:

OPTIONS of 'https://server/svn/repo': authorization failed: Could not authenticate to server: rejected Basic challenge (https://server)

This happens whether I have the DefaultCredentials set below or not:

using (SvnClient client = new SvnClient())
{
//client.Authentication.DefaultCredentials = new System.Net.NetworkCredential("user", "password");
client.LoadConfiguration(@"C:usersmyuserAppDataRoamingSubversion");
SvnUpdateResult result;
client.Update(workingdir, out result);
}