It turns out that when saving credentials in the RAS connection there is a setting that must be enabled on the DotRas dialer, otherwise it seems to attempt to dial without any credentials.
public bool Connect(string dialerEntryName)
{
string path = RasPhoneBook.GetPhoneBookPath(RasPhoneBookType.User);
using (RasDialer dialer = new RasDialer())
{
dialer.EntryName = dialerEntryName;
dialer.PhoneBookPath = path;
dialer.AllowUseStoredCredentials = true;
dialer.Dial();
return true;
}
}
The connection works with the setting:
dialer.AllowUseStoredCredentials = true;
Added. I assume that manually specifying credentials will also work, but I have not confirmed this.