The main questions that tend to come up in C# Architect interviews relate to:
1) Event Life Cycles
2) Basic Design Patterns, usually with a focus on data management.
3) Inheritance, polymorphism and encapsulation
4) Interfaces, virtual methods and overrides.
5) Delegates and threads. If its asp.net they usually don't ask many questions about threading.
6) Data access and storage.
7) Code Management and Build Processes.
8) Methodologies. Try to stay neutral on these as they are like religion.
9) OR/Ms. Again, try to stay neutral on these.
There are other areas depending on the type of project they are working on as well, e.g. WPF, Silverlight, MVC.