title: Operation is not valid due to the current state of the object, when I select a dropdown list
body: <h2>I have radcombo boxes on aspx page, and when I select any option from then it gives error`Server Error in '/' Application.</h2>
  <p>Operation is not valid due to the current state of the object.
  Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.</p>
  <blockquote>
  <p>Exception Details: System.InvalidOperationException: Operation is not
  valid due to the current state of the object.</p>
  </blockquote>
  <p>Source Error:</p>
  <blockquote>
  <p>An unhandled exception was generated during the execution of the
  current web request. Information regarding the origin and location of
  the exception can be identified using the exception stack trace below.</p>
  </blockquote>
  <p>Stack Trace:</p>
  <blockquote>
  <p>[InvalidOperationException: Operation is not valid due to the current
  state of the object.]<br />
  System.Web.HttpValueCollection.ThrowIfMaxHttpCollectionKeysExceeded()
  +2692302    System.Web.HttpValueCollection.FillFromEncodedBytes(Byte[] bytes, Encoding encoding) +61<br />
  System.Web.HttpRequest.FillInFormCollection() +148</p>
  <p>[HttpException (0x80004005): The URL-encoded form data is not valid.]
  System.Web.HttpRequest.FillInFormCollection() +206<br />
  System.Web.HttpRequest.get_Form() +68<br />
  System.Web.HttpRequest.get_HasForm() +8735447<br />
  System.Web.UI.Page.GetCollectionBasedOnMethod(Boolean dontReturnNull)
  +97    System.Web.UI.Page.DeterminePostBackMode() +63    System.Web.UI.Page.ProcessRequestMain(Boolean
  includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
  +133</p>
  </blockquote>
  <hr />
  <blockquote>
  <p>Version Information: Microsoft .NET Framework Version:2.0.50727.3634;
  ASP.NET Version:2.0.50727.3634 `</p>
  </blockquote>