Type 'System.Collections.Generic.IDictionary`2[[System.String, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089],[System.Object, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]' is not supported for deserialization of an array.

So I was getting this error when calling a page method from jquery. Google turned up quite a few variations but not the exact string, and the suggestions associated with those variations were not relevant. It turned out that in my case the data packet I was sending in the jquery ajax call was wrong. I had code like this:

MyParam = []; ... $.ajax({ type: 'POST', url: document.location.pathname + '/DoSomething', data: JSON.stringify(MyParam), contentType: "application/json; charset=utf-8", dataType: "json", complete: function (a, b, c, d) { console.log(a, b, c, d); } });

and my page method looked like this:

[WebMethod()] public static void DoSomething(List<s> B) { B.ToString(); }

fairly simple but there are 2 things wrong with this. The first problem was the data - I hadn't named the paramater

so the fixed javascript code looks like this:

MyParam = []; ... $.ajax({ type: 'POST', url: document.location.pathname + '/DoSomething', data: JSON.stringify({B:MyParam}), contentType: "application/json; charset=utf-8", dataType: "json", complete: function (a, b, c, d) { console.log(a, b, c, d); } });

The second problem was it turns out the .NET javascript seraliser doesn't like List<t> so a quick change to the C# fixed that.

[WebMethod()] public static void DoSomething(S[] B) { B.ToString(); }

So in summary - make sure you pass an object with named parameters as the data argument - not simple the content of the only parameter!