Twitterizer is not maintained anymore and not compatible with Twitter API 1.1.
Details about Twitter API 1.1: blog
From Official page:
Will applications using Twitterizer stop working?
Not right away, no. I have no power to stop the code or binaries that are already in use from working, nor would I want to. However, the current version of Twitterizer uses version 1.0 of the Twitter API which is scheduled for death in March 2013. At that time, I cannot speak to any functionality.
What am I supposed to do now?
As I see it, you have three options: jump to a new library, make Twitterizer your own, or roll your own.
Twitterizer source code will remain available in its current state. I encourage you to download the source and make it your own.
If you'd rather not take that on, there are a couple of other fantastic libraries. For example: Linq2Twitter and TweetSharp
As said above you need to find a new library compatible with Twitter API 1.1, as Linq2Twitter or TweetSharp.