I am having problems with a css/js drop down menu I have placed in the cart when it comes to https pages. I get the following message:

this page contains both secure and nonsecure items

Searching various forums on the web this seems to be a common problem, although I couldn't find an answer to fix my problem.

Code:
<script type="text/javascript" src="https://www.website.com.au/menu/menu.js"> </script>
Now with this above line, if I remove it, I no longer get the message, but the the drop down part of the menu doesn't function. I had thought perhaps something in the js file was causing this issue, but after I deleted the entire contents of the js file and uploaded the blank file, the same problem still occured.

Any ideas how to fix this?