Well after talking to their recruiter, I'll set up for a technical interview.

The technical interview was actually surprisingly simple conceptually. I was expecting something really difficult, maybe a hard algorithm or something, but it was just a multi-value dictionary. How to implement it is very obvious for any seasoned developer. However, the coding environment you have to use is buggy; Intellisense didn't work, forcing me to pull up the documents for common types. Despite all that, I still completed the exercise in the allotted time, just off balance from the environment.

The information given to me said using documentation was okay, but it seems that and perhaps not being at home with the coding environment will get you disqualified.

Implement a multi-value dictionary class.