How to fix magento shopping cart add to wishlist bug in ie?

I am working on a magento project with a custom made sign editor. Everything works fine except for the add to wishlist function in the shopping cart. It works fine on firefox but on ie it does not add the product on the wishlist. I can't figure out what's wrong with it.

I have used firebug on firefox to check if there are some javascript errors but there is none.

Internet Explorer version: 7 & 8 Magento Version: 1.4.1

errors on ie only:

1. Object doesn't support this property or method cart, line 1 character 1
2. Object expected cart, line 462 character 1
3. Object doesn't support this property or method signpreview, line 46 character 2
4. Object doesn't support this property or method updatePost, line 46 character 2
5. Object doesn't support thi开发者_开发技巧s property or method signpreview, line 46 character 2

Any help would be very much appreciated.

These are not Magento errors - 'signpreview' and 'updatePost' do not look like anything in the Magento codebase.

Have you swapped over to the default theme and seen if you can add to wishlist? If that works then it is a theming problem, not a products or Magento problem.