Since our application is running in WebFarm we are using Captcha by storing in the Session as described in the Telerik doc. But after doing so we are seeing lots of errors in log related to that. Can anyone help in fixing this error. Telerik AJAX version 2013.2.717.40
System.NullReferenceException: Object reference not set to an instance of an object.
at Telerik.Web.UI.Captcha.SessionCachingProvider.Clear(String key)
at Telerik.Web.UI.Captcha.BaseCaptchaCachingProvider.CacheExpirationCallback(String key, Object value, CacheItemRemovedReason reason)
at System.Web.Caching.CacheEntry.CallCacheItemRemovedCallback(CacheItemRemovedCallback callback, CacheItemRemovedReason reason)