Single posts are not shown

Hi,

First of all: love the plugin. It worked great, till about a week or so…
The main language of the website is Dutch. The second language is English.
All pages and posts are linked to eachother and all settings are shown in this image (I have not fiddled with them after the initial installation).
http://imageshack.us/photo/my-images/845/g9bj.png/

The problem is that the the single posts can’t be read when starting from the second language blog or newspage. Also when switching from language within a first language single post, nothing is shown as you can see when looking at http://www.yochiver.be/beige-labradorreutje-monter-yochiver/ (in first language Dutch) and same post, linked to this post http://www.yochiver.be/yellow-male-labrador-monter-yochiver/ (in second language, English)

After contact with the theme developer, he said his theme ought to work with the plugin as he didn’t see an immediate issue so far.

Any ideas where we need to look in order to solve this?

Thanks so much!!!

http://ww.wp.xz.cn/plugins/polylang/