Using Plugins for events not working

I love these responsive themes,and am admittedly a newbie to WordPress and these responsive themes….
I am trying to add a community events calendar to my WordPress site which uses the Classifieds Responsive them. I have tried using several of the plugins found on the wordpress plugin area – including the AJAX Event Calendar and the Event Organiser plugins.
They both install and activate ok, and the AJAX Event Calendar works great and as expected..however it messes up something in the Classified Responsive theme so that I cannot open messages in the My Account -> My Messages area with the plugin activated/working.
In the case of the Event Organiser event calendar plugin, it installs and activates ok and does NOT mess up any functionality in the Responsive Classifieds theme, however, it will not work correctly…when you click on a day in the full calendar view to add a new event entry to that day, it pops up a modal window for you to enter the event, but it disables any mouse input.
I have similar problems with other plugins – i was using a modal window plugin (Easy Modal) to pop up some pages in a modal window, and in using that plugin, it also disables or interferes with the messages in the My Account -> My Messages area – you can’t open the messages.
Does anyone know what might be causing these types of issues….the common thread seems to be the plugins i’m trying to use are using ajax or modal windows to pop up my pages/forms.