Can you create a fiddle with this breaking?
It looks like $ is defined, but each isn't there, which is very weird. Do you modify $ or include any jQuery plugins?
can.$ is an internal reference to the current DOM library (jQuery in your case) and points to the same thing as can.each, which is the preferred method to use. Using can.each, can.ajax, etc makes it easier to deal with API changes in the underlying library and makes it less of a headache to swap out the library in the future.