Kentico Message: The CSRF cookie was missing

Question

I have a website built with K12.095 version.(Webform) There is tons of line in event log that says below error:

Message: The CSRF cookie was missing.

Exception type: CMS.Protection.Web.UI.CsrfException

Stack trace: at CMS.Protection.Web.UI.CsrfProtection.EnsureCsrfToken() at CMS.Protection.Web.UI.CsrfProtection.OnPostMapRequestHandlerExecute(Object sender, EventArgs eventArgs)

at CMS.Base.AbstractHandler.CallEventHandler[TArgs](EventHandler1 h, TArgs e) at CMS.Base.AbstractHandler.Raise[TArgs](String partName, List1 list, TArgs e, Boolean important)

at CMS.Base.SimpleHandler2.RaiseExecute(TArgs e) at CMS.Base.SimpleHandler2.StartEvent(TArgs e) at

System.Web.HttpApplication.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() at System.Web.HttpApplication.ExecuteStepImpl(IExecutionStep step) at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

Even tough I can see the cookie named 'CMSCsrfCookie' is set to browser, I still have the error. What is the reason behind this? How can I solve the error? Thanks.