I installed iSearch on a clean OpenCart v1.5.6 install and when enabling the extension, a error is thrown for the iSearch JS and prevents anything else from working on the page that needs JS. See screenshot for the error: https://www.dropbox.com/s/lqh6gfd6jminkq1/isearch_issue.png 

Can you make sure you have installed the latest version of iSearch (3.2.2)?

Ouch ... it's using version 3.1.6. I contacted the person who purchased the extension to download me the most recent version. Thanks for the speedy reply ... I'll do the update somewhere tomorrow and let you know outcome!

Sure, updating should do the trick.