Calling many web services asynchronously
I'm not all that familiar with async/await (I really need to get going on this), but I find your code pretty clear, except why the magic number  5 is being used for an initialCount.

I like your usage of var, but the comments are a little redundant, they say nothing much that the code doesn't already tell.

It would have been nice to see the actual code in place of the placeholder comments in the try block - I'd expect to see a method call here; if that comment stands for code that actually implements what's described, you need to factor it out.

Also I would have indented the async task's body, but that's more of a nitpick.

I would probably also have introduced a var validOrders = orders.Where(order =&gt; !order.HasError); to make the foreach loop clearer. Not sure I like x for a name in the lambda: try to use meaningful names everywhere.