Can you please add the error message (if there are any) from the log.

I guess that the problem is that the database and site are out of sync (new code with old database)

Hi,

Make sure that the current language is selected as available lanaguage under "Available Languages" option in edit mode. 

Hi, 

After I enabled the EPiServer Logs, I found the following log:

2014-08-07 16:03:08,516 ERROR [6] EPiServer.Global.Global_Error - 1.2.5 Unhandled exception in ASP.NETSystem.Web.HttpUnhandledException: Exception of type 'System.Web.HttpUnhandledException' was thrown. ---> System.ArgumentException: Invalid postback or callback argument.  Event validation is enabled using 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.DropDownList.LoadPostData(String postDataKey, NameValueCollection postCollection)   at System.Web.UI.WebControls.DropDownList.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)   --- End of inner exception stack trace ---   at System.Web.UI.Page.HandleError(Exception e)   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)   at System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)   at System.Web.UI.Page.ProcessRequest()   at System.Web.UI.Page.ProcessRequestWithNoAssert(HttpContext context)   at System.Web.UI.Page.ProcessRequest(HttpContext context)   at ASP.admin_cms_edit_editpanel_aspx.ProcessRequest(HttpContext context) in c:\Windows\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\root\0354437c\8d5ae44f\App_Web_t4r5vesf.0.cs:line 0   at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

You have som problem with the postback that the IIS does not like, try to do like the errormessage say, go into the web.config and search for  and change it to  and see what is happening

Thanks for your reply Henrik.

I'm able to publish the pages now.

I never expected the EnableEventValidation stops the page publishing from EPiServer CMS.

Have a good day :)

There is a faq about it here:
http://world.episerver.com/FAQ/Items/Event-validation-is-enabled-causing-invalid-postback/

Glad that it works