I was right, it is a javascript problem.
It is caused by the fact that you are using K2 with a module that uses JQuery, mod artbook. This causes the following error in one of the scripts that K2 uses:-
Error: $("comment-form").addEvent is not a function
Source File:
aecpathfinders.org/components/com_k2/js/k2.js
Line: 13
The problem though is caused by mod artbook, modules that use JQuery should include the noconflict() function that should prevent this sort of thing from happening. It's am example of poor quality extension writing.
Basically you have two choices: you can disable the K2 plugin, this will stop the scripts from K2 loading. Then the error will no be generated.
Or you can not use mod artbook.