This is a pretty rookie mistake with .NET 4.5 and the new async / await operators.  While searching for the answer I found a lot of noise and no valuable answers so I thought I would notate the solution on my blog.

The short answer is that any method that uses await must itself be marked with async.

Take this code for example:

Error    2    The ‘await’ operator can only be used within an async method. Consider marking this method with the ‘async’ modifier and changing its return type to ‘Task’.