It seemed to have something to do with my using the WordPress plugin “Quick Cache (Speed without compromise)”
After disabling this plugin, the Google Calender events is working just fine again..
But to answer your question :), no it happened every time i view’ed the site, i had to login to the admin area and update one of my feeds to make the problem disapear…
then when i logged out of the admin area again, it still worked, until i viewed the site in a new session..
i’ll try the W3 cache thing later, and se it works together with the Google Calender events plugin.