entity framework 4 - Dbcontext with using-clause in Asp.Net Json-Call -

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i ran problem when switching local development server local iis server (asp.net mvc4) using following controller-method:

  public jsonresult getjsondata(string context, string language)       {        using (keyvaluedbcontext db = new keyvaluedbcontext())        {              var entries = u in db.keyvalues                           ((u.context == context) && (u.language == language))                           select u;              return json(entries, jsonrequestbehavior.allowget);       }     }

using local server, received data when calling method javascript without problem. method retrieves collection of key-value pairs database repository , sends them client). after switching iis got exception telling me dbcontext had been disposed of (although using clause ends after return-statement). (nb: visual studio not able find jsonserializer.cs reason, when error occurred). switching following version solved problem completely: 

public jsonresult getjsondata(string context, string language)        {         keyvaluedbcontext db = new keyvaluedbcontext();         var entries = u in db.keyvalues                      ((u.context == context) && (u.language == language))                      select u;          return json(entries, jsonrequestbehavior.allowget);    }

in both cases, using-block:

  using system;   using system.collections.generic;   using system.data;   using system.data.entity;   using system.linq;   using system.web;   using system.web.mvc;   using beepov4.models; // project-models

my question: acceptable way use dbcontext purpose of json-calls (and dropping using-clause) or there particular downside or hidden problem should aware of?

try reading entries memory entries.tolist() before passing them json():

using (keyvaluedbcontext db = new keyvaluedbcontext()) {         var entries = u in db.keyvalues                       ((u.context == context) && (u.language == language))                       select u;          return json(entries.tolist(), jsonrequestbehavior.allowget); }

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