'Operation is not valid due to the current state of the object' error during postback

Question

Somebody posted quite a few form fields to your page. The new default max introduced by the recent security update is 1000.

Try adding the following setting in your web.config's <appsettings> block. in this block you are maximizing the MaxHttpCollection values this will override the defaults set by .net Framework. you can change the value accordingly as per your form needs

<appSettings>
    <add key="aspnet:MaxHttpCollectionKeys" value="2001" />
 </appSettings>

For more information please read this post. For more insight into the security patch by microsoft you can read this Knowledge base article

I didn't apply paging on my gridview and it extends to more than 600 records (with checkbox, buttons, etc.) and the value of 2001 didn't work. You may increase the value, say 10000 and test.

<appSettings>
<add key="aspnet:MaxHttpCollectionKeys" value="10000" />
</appSettings>

For ASP.NET 1.1, this is still due to someone posting more than 1000 form fields, but the setting must be changed in the registry rather than a config file. It should be added as a DWORD named MaxHttpCollectionKeys in the registry under

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\ASP.NET\1.1.4322.0

for 32-bit editions of Windows, and

HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\ASP.NET\1.1.4322.0

for 64-bit editions of Windows.

If your stack trace looks like following then you are sending a huge load of json objects to server

Operation is not valid due to the current state of the object. 
    at System.Web.Script.Serialization.JavaScriptObjectDeserializer.DeserializeDictionary(Int32 depth)
    at System.Web.Script.Serialization.JavaScriptObjectDeserializer.DeserializeInternal(Int32 depth)
    at System.Web.Script.Serialization.JavaScriptObjectDeserializer.BasicDeserialize(String input, Int32 depthLimit, JavaScriptSerializer serializer)
    at System.Web.Script.Serialization.JavaScriptSerializer.Deserialize(JavaScriptSerializer serializer, String input, Type type, Int32 depthLimit)
    at System.Web.Script.Serialization.JavaScriptSerializer.DeserializeObject(String input)
    at Failing.Page_Load(Object sender, EventArgs e) 
    at System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e)
    at System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e)
    at System.Web.UI.Control.OnLoad(EventArgs e)
    at System.Web.UI.Control.LoadRecursive()
    at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

For resolution, please update your web config with following key. If you are not able to get the stack trace then please use fiddler. If it still does not help then please try increasing the number to 10000 or something

<configuration>
<appSettings>
<add key="aspnet:MaxJsonDeserializerMembers" value="1000" />
</appSettings>
</configuration>

For more details, please read this Microsoft kb article