Dear Ross,
That was a very quick and very precise reply. Thanks a lot.
I totally missed the error console, but even if I would have had a look at it, I guess, I never made a link between lightbox and the google calendar.
I did fix the Lightbox Plugin by altering the following 3 lines in lightbox-gallery/lightbox-gallery.js.
from
jQuery('a[rel*=lightbox]').lightBox();
jQuery('.gallery a').tooltip({track:true, delay:0, showURL: false});
jQuery('.gallery1 a').lightBox({captionPosition:'gallery'});
to:
if (jQuery('a[rel*=lightbox]').length > 0) jQuery('a[rel*=lightbox]').lightBox();
if (jQuery('.gallery a').length > 0) jQuery('.gallery a').tooltip({track:true, delay:0, showURL: false});
if (jQuery('.gallery1 a').length > 0) jQuery('.gallery1 a').lightBox({captionPosition:'gallery'});
In order to avoid accessing "undefined" pointers (e.g. when the result of the query is empty).
With that code fixed, the google calendar plugin is performing just fine.
I tried to contact the plugin author and provide this information as well, so hopefully others can benefit from the fixed code too.
Regards
Adrian