How can I use Debug.Write with dynamic data?

You’re being bitten by your use of var here, is my guess.

I’m assuming that Contents is dynamic.

Consider this example:

dynamic d = null;
var s = d.ToString();

s is dynamic not string.

You’ll want to cast the object to object before calling ToString, or cast the result of ToString to a string. The point is that at some point, somewhere, you need a cast to get out of the dynamic cycle.

This is how I’d solve it:

string str = ((object)frame.Contents).ToString();
Debug.WriteLine(str);

or

string str = frame.Contents.ToString() as string;
Debug.WriteLine(str);