Did you have to make any modifications? I installed Zen Cart, then IH and the Winchester Black template which has Colorbox built in and it is giving IH some problems.
Winchester Black has Zen Lightbox not Zen Colorbox.. You will need to post your issue on the template authors support thread..
My Site - Zen Cart & WordPress integration specialist I don't answer support questions via PM. Post add-on support questions in the support thread. The question & the answer will benefit others with similar issues.