Langue bar faulty; broken link from one language to the other

Hi, my site is bilingual. From the home page, clicking on the flags work; however, once when you’re reading the article in English and click on the French flag to read the French version, goes to 404 page not found.

The flag icon at the bottom of the page seems out os sinc, you can only see the English flag. How to I get back the French flag as well?

Thanks.

(I have another questions concerning drop down menu problem which I don’t think is linked, so I’ll post that with a different title for clarity. However, perhaps that problem does have something to do with the above….)