Intermittent permalink error!

Hi,

I’m trying to resolve a problem on a site I didn’t make (I’m not a programmer).

Site is available in French and English and the error happens only when navigating in French.
Everything works fine when I’m in the English environment and this error only started when I created two new categories, one in English and one in French.

I have 2 widgets in a sidebar that display titles of posts, in 2 different blogs (category).

On 3 out of 4 clicks, links work fine but from time to time, the permalink takes me to the English page of the blog, with an empty page.

I’m using the /index.php/%year%/%monthnum%/%postname%/ permalink structure.

Any idea anyone?