Hi,
I'm sorry, but i have already answer you that issue may be with your site template.
What i told you just before does not need to be a developer, but to check options of your site template, and if one option is to disable the css compression
In case you don't find it, better to contact the site template developer, as i don't know how this one works, and don't have time to check and tests all site templates that exist in the market!
All i could do was to check your site online, and see that there was issue with your site template, a css compression, and Google Maps. (nothing related directly to iCagenda...)
Hope this helps ?
But i recommend you to check options of site template, and if you can't find the option to contact its developer or check if a documentation on how to disable css and script compression on your site template.
But for sure, i will recommend you to ugrade your site template, and if no update availabel, to change your site template, as your site template is NOT well coded for JOOMLA 3! (so, that's maybe why this one works only on Joomla 2.5).
Thank you,
Best Regards,
Cyril