What does NSURLErrorDomain error -999 mean?

I tried logging in manually, but it said it doesn't exist, even though it works when I log in through my browser.

What does NSURLErrorDomain error -999 mean?

I tried logging in manually, but it said it doesn't exist, even though it works when I log in through my browser.

Update: I don't know if this will help. (Originally I was going to upload images, but I only have 1 rep, so I'll just describe it in detail).

1. I open up the app and I get a screen similar to the SE log in web page and click on "log in with Stack Exchange"
2. Then the window "The operation couldn't be completed. (NSURLErrorDomain error -999.) pops up. It gives me one option, which is to click "OK".
3. Next the Stack Exchange Notifier window says "Third Party Cookies Appear To Be Disabled", "You can continue and log in manually however." I log in manually.
4. Stack Exchange OpenID window shows up and I log in. Then it says "Not Found", "This page could not be found."

But I'm able to log in through my browser, so I don't know why it says that.