New Post: V3.2 default.aspx Line 50 'Object Ref Not Set' Reason ?

Hi,
Sometimes my development site errors and after a while actually clears itself of the error without me actually doing anything !!

The message which appears in the browser is:

object reference not set to an instance of an object: 
PageNode homePageNode = sitemapNavigator.HomePageNodes.FirstOrDefault();

on the default.aspx page line 50

My C1 build version is Build no. 3.2.4497.34793

Does somebody know why this is happening? and what should I do to stop it from occuring?

Thanks in advance.
Martin.