Help me please!

[Guest]

I've installed the system as your manual, but when I clicked one of the links on the home page, the following error message occurred, which read, "

Fatal error: Unknown(): The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition navigationhistory of the object you are trying to operate on was loaded _before_ the session was started in /home/jennypei/testing.networkdictionary.com/docs/BruceIPN/catalog/includes/application_top.php on line 309"

 

Please tell how to debug now, thanks in advance!