Hi,
1st possibility:
Your website is having a JAVA conflict problem which prevents our Zoom Effect works properly.
If you provide me a LIVE URL which links to your any product details page in your website, i can point out the problem.
2nd possibility,
You forgot to publish the "Flexible - Zooming Effect" module. OR you published it but you set a position that doesn't exist in your joomla template. Publish it in the position that you are SURE that it is exist in your joomla template. The most proper position is usually "footer", "left" or "right" positions, because almost every joomla template has those positions.
cheers.