Windows 7: Windows 7 web page conundrum

Couldn't find this on the forum so apologies of I missed it. I am having a problem displaying a javascript menu in ie8 running on windows 7. The menu simply won't display at all and ie8 reports an unspecified script error which I have tried to debug but to no avail. I have also checked the security and compatibility settings without success.

On the same system I also have Opera installed and the web page menu displays perfectly (obviously - it is Opera!).

I'm not certain Internet Explorer is the problem as my old xp computer has ie8 installed and displays the web page menu without error which may suggest it's Windows 7 that's the problem?

Confusingly, on the same web page I have swf animations placed above the javascript menu yet if I place the menu above the swf or remove the swf animations altogether the page will display correctly without errors!

To conclude: Why can't Windows 7 and Internet Explorer display a javascript menu below an embedded Flash swf ??

Appreciate any suggestions...