This error might be caused by a bug, which wasn't fixed until the 4.1 version of Kentico. Could you please try the following approaches?
A) Could you please check the files in ~\App_Data\CMSModules\WebAnalytics
if there are all in the right format, if you are using the webanalitics module?
B) Could you please try to follow procedure bellow:
1. Open App_Code folder
2. Make backup of Global.asax.cs file
3. Open Global.asax.cs file in VS or any text editor
4. Navigate to line approximately 667
5. Change this code:
// Get passive timer and execute
SchedulingTimer timer = SchedulingTimer.EnsureTimer(siteName, false);
to this code
// Flush the output
// Run scheduler actively within the request
string serverName = SettingsHelper.AppSettings["CMSWebFarmServerName"];
C) Could you please also try to display ~\CMSPages\scheduler.aspx page with and without 'www' prefix in your domain name and let me know what you see on this page?