asp.net - JavaScriptSerializer Error Message - Duplicate type, how do I resolve? -

I am trying to sort some stars and come back through an AJAX call and I see a strange error giving. Any help would be greatly appreciated:

  Compiler error message: & lt; / B & gt; CS0433: 'System.Web.Script.Serialization.JavaScriptSerializer' type exists in both 'c: \ WINDOWS \ assembly \ GAC_MSIL \ System.Web.Extensions \ 1.0.61025.0__31bf3856ad364e35 \ System.Web.Extensions.dll' and 'c : \ WINDOWS \ Assembly \ GAC_MSIL \ System.Web.Extensions \ 3.5.0.0__31bf3856ad364e35 \ System.Web. Extension to DL ' 

I found the resolution: Using code for a JavascriptSerializer One Placing exceptions when used within the webform, place a class call in a web service and it worked perfectly. Maybe there are some restrictions on the class?!