Roel,
We don't have have a ready answer - this may take a while to figure out. At a glance, it's breaking at "var pageTracker = _gat._getTracker("UA-703424-15");", with "_gat" being not initialized (null). Please check
HttpVPN compatibility article - it may be of help. We'll take a look, but if you know where _gat variable is defined, you should be able to tell which script has not been loaded. Comparing HTML source of the page with and without HttpVPN should give you a good idea about what may be wrong.
Best regards,
UltiDev Team.
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