Help Deserializing Dictionary returned from ASP.NET page to C# App

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C#

ASP.NET

I am messing around with a spell checker and I am having a problem De-serializing a dictionary of misspelled words and their suggested spellings. An application sends text to an ASP.NET page. The ASP app performs spell checking and returns a dictionary with the Keys being the misspelled words along with a List of correct suggestions.
Error that I am receiving in VS 2010 when ser.Deserialize is called:

An unhandled exception of type 'System.ArgumentException' occurred in System.Web.Extensions.dll
Additional information: Invalid object passed in, member name expected. (1): {"missspelled":["misspelled","miss spelled","miss-spelled","misspelling","misspell","dispelled","misspecified"],"wrods":["words","rods","woods","prods","w rods"]}

For the life of me I cannot figure out why the runtime is complaining. Any help would be appreciated.

ASP.NET code

Dictionary<string, List<string>> WordSuggestions = new Dictionary<string, List<string>>();
...
Populate dictionary with misspelled words and list of suggestions
...
//JSON encode Dictionary and return.
JavaScriptSerializer serializer = new JavaScriptSerializer();
string jsonresult = Server.HtmlEncode(serializer.Serialize(WordSuggestions));
Response.Write(jsonresult);

Data as seen/received by App

{"missspelled":["misspelled","miss spelled","miss-spelled","misspelling","misspell","dispelled","misspecified"],"wrods":["words","rods","woods","prods","w rods"]}

C# App Code (ReturnedSpelling holds the "Data as seen by App" as seen above.

JavaScriptSerializer ser = new JavaScriptSerializer();
MispelledWords.text = ser.Deserialize<Dictionary<string, string[]>>(ReturnedSpelling);

MispelledWords.text is an appropriate dictionary of type

Dictionary<string, string[]>;

One thing I just noticed is that in the ASP app, my Dictionary is:

Dictionary<string, List<string>> 

and my C# app is:

Dictionary<string, string[]> 

Although I can't see why this would be a problem after it has been serialized.

...

I have since changed my dictionary

string[] to List<string>

on my application (receiving) side. It still does not work...as I suspected. I am serializing then encoding then sending and when the data is returned, decoding and de-serializing in that order.

This is what I am using on my application side:

Encoding...

HttpUtility.UrlEncode

Decoding...

HttpUtility.UrlDecode