Most answers to this questions suggest to make sure your Twitter app is setup as a "web app" and not a "desktop app"... in the current Twitter dev site... I do not see this option.
I also made sure to provide a callback URL when first setting up my app.
Any thoughts?
The API returns a 401 when the OAuth tokens you've provided are revoked/invalid or any time you attempt an action for which you do not have access. For example, if your application is read-only and it attempts to post a tweet, a 401 will be returned.
Twitter does provide an error message and Twitterizer will return that to you when it can. It is in the ErrorMessage property of the response.