I've just upgraded an intranet solution and came across an error I have problem locating. In viewmode the page works well, but when I'm entering edit mode I get the error below.

log4net:

2013-11-06 01:08:39,877 ERROR [48] EPiServer.Global.Global_Error - 1.2.5 Unhandled exception in ASP.NET
System.Web.HttpUnhandledException (0x80004005): Exception of type 'System.Web.HttpUnhandledException' was thrown. ---> System.NullReferenceException: Object reference not set to an instance of an object.
   at EPiServer.UI.Edit.EditPageButtonControl.OnPreRender(EventArgs e)
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
   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.ProcessRequest(HttpContext context)
   at ASP.cmsui_cms_edit_editpanel_aspx.ProcessRequest(HttpContext context) in c:\Windows\Microsoft.NET\Framework64\v4.0.30319\Temporary ASP.NET Files\root\2c2f7174\4aa0d3ba\App_Web_ihgk4flu.2.cs:line 0
   at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

Error and stack trace:

Object reference not set to an instance of an 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.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:

Stack Trace:

[NullReferenceException: Object reference not set to an instance of an object.]
   EPiServer.UI.Edit.EditPageButtonControl.OnPreRender(EventArgs e) +456
   System.Web.UI.Control.PreRenderRecursiveInternal() +112
   System.Web.UI.Control.PreRenderRecursiveInternal() +221
   System.Web.UI.Control.PreRenderRecursiveInternal() +221
   System.Web.UI.Control.PreRenderRecursiveInternal() +221
   System.Web.UI.Control.PreRenderRecursiveInternal() +221
   System.Web.UI.Control.PreRenderRecursiveInternal() +221
   System.Web.UI.Control.PreRenderRecursiveInternal() +221
   System.Web.UI.Control.PreRenderRecursiveInternal() +221
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +4200