Well,

You are a using a very too old iCagenda version...

You should update it (as well as Joomla).
If you check the changelog, you will see all changes and bug fixes for iCagenda, and some for iCagenda on Joomla 2.5.

You have one of this, but if you keep working on an old outdated Joomla with an outdated iCagenda version, i can't help you as you are already working on a vulnerable system (check security patches of Joomla, and it's really better to upate to Joomla 3).

But definitly, no sites should run an iCagenda version outdated (or at least, older than the 3 serie). (Check security patches for iCagenda by the past, and you will understand why).

All your client site is 6 years old, and you will save a lot of time yourself by just updating Joomla and all the extensions!

Best regards,
Cyril