I embbeded   code of signup page of newsletter , And all fields are displaying like name, email subscribe button etc.

When I fill the form it show:  " server error has occurred while trying to process your request.      "

I login in admin panel and found followoing error in system log:

2014-08-24 13:20:46,859 ERROR 117.220.224.58 - en-US - /subscribe.aspx - mojoPortal.Web.Global -  Referrer(http://zssindia.com/subscribe.aspx) useragent Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Firefox/31.0 
System.ArgumentException: Invalid postback or callback argument.  Event validation is enabled using <pages enableEventValidation="true"/> in configuration or <%@ Page EnableEventValidation="true" %> in a page.  For security purposes, this feature verifies that arguments to postback or callback events originate from the server control that originally rendered them.  If the data is valid and expected, use the ClientScriptManager.RegisterForEventValidation method in order to register the postback or callback data for validation.
   at System.Web.UI.ClientScriptManager.ValidateEvent(String uniqueId, String argument)
   at System.Web.UI.Control.ValidateEvent(String uniqueID, String eventArgument)
   at System.Web.UI.WebControls.HiddenField.LoadPostData(String postDataKey, NameValueCollection postCollection)
   at System.Web.UI.WebControls.HiddenField.System.Web.UI.IPostBackDataHandler.LoadPostData(String postDataKey, NameValueCollection postCollection)
   at System.Web.UI.Page.ProcessPostData(NameValueCollection postData, Boolean fBeforeLoad)
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
2014-08-24 13:20:55,859 INFO (null) - (null) - (null) - mojoPortal.Web.WebTaskManager - started WebTaskManager task 

does i have to flip or tweak any add key value in web config file ??

Thanks in advance.