Using a c# variable of type dynamic in embedded code

The Direct Answer

Actually this issue is that Annonymous types don't have public properties, they have internal properties. An Aspx is compiled into a separate assembly so when you try to dynamically invoke it doesn't see the property is there because it's marked as internal you don't have access from where you are calling. The quickest simplest solution is to use an ExpandoObject instead of an Anonymous object.

public dynamic showMe
    {
        get
        {
            dynamic exp = new ExpandoObject();
                exp.val1 = 5,
                exp.val2 = "This is val2",
                exp.val3 = new List<int>(){1,2,3,4,5}
            return exp;
        }
    }

Just in case

Another solution if you really want to use anonymous objects is to use ImpromptuInterface you do have to declare an interface but you get static typing without creating dummy classes. It creates a lightweight proxy that forwards invocations using the dlr in the context of the original assembly it's a lot faster than reflection.

interface IMyInterface{
    int val1 {get;}
    string val2 {get;}
    IList<int>val3 {get;}
}

public IMyInterface showMe
    {
        get
        {
            return new
            {
                val1 = 5,
                val2 = "This is val2",
                val3 = new List<int>(){1,2,3,4,5}
            }.ActLike<IMyInterface>();
        }
    }