Operation is not valid due to the current state of the object.

Error : Operation is not valid due to the current state of the object.

Stack Trace:

[InvalidOperationException: Operation is not valid due to the current state of the object.] System.Web.HttpValueCollection.ThrowIfMaxHttpCollectionKeysExceeded() +2692482 System.Web.HttpValueCollection.FillFromEncodedBytes(Byte[] bytes, Encoding encoding) +61 System.Web.HttpRequest.FillInFormCollection() +148 [HttpException (0x80004005): The URL-encoded form data is not valid.] System.Web.HttpRequest.FillInFormCollection() +206 System.Web.HttpRequest.get_Form() +68 System.Web.HttpRequest.get_HasForm() +8743911 System.Web.UI.Page.GetCollectionBasedOnMethod(Boolean dontReturnNull) +97 System.Web.UI.Page.DeterminePostBackMode() +63 System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +133

This error occurs when form fields are very large in numbers.By default, the maximum value of MaxHttpCollection is 1000.

Solution:

To solve this error, increase MaxHttpCollection value. Try adding the following setting in your web.config's <appsettings> block. 

<appSettings>
        <add key="aspnet:MaxHttpCollectionKeys" value="3000" />
 </appSettings> 

you can change the value accordingly as per your need.