Having same issue, get the same error even when I fill the domain/username/password fields

When I add in the user/pass in the existing configuration it works, though my password changes often enough it is obnoxious to need to update it there where my proxy supports NTLM auth automatically.

It would be nice to not have to enter the credentials at all - for example, consider the following code:

var wc = new System.Net.WebClient();
wc.Proxy.Credentials = System.Net.CredentialCache.DefaultCredentials;
wc.DownloadString("http://linqpad.net").Dump();

This works like a champ behind our proxy that requires authentication. Without setting up the Proxy Crendentials property, it throws a WebException with the message "The remote server returned an error: (407) Proxy Authentication Required."

Maybe do a check for a 407, and try the default credentials but still allow for custom proxies / credentials through the UI?

What happens when you enter your proxxy username/password/domain in the textboxes provided?