I'm looking into it guys. The trailer passed the FSUK test which is why it was approved and works for many people, so most likely it is a mod conflict with a mod you have that you got from somewhere other than FSUK.
In most cases it is caused by different versions of beleuchtungV3 being used in your mods.
You have to edit the F350 found on this site. It is using FS11 attacher joints. The trailer is using FS13 attacher joints, because...... shocker, it's a FS13 mod.
Try using it with Giants siga dolly and a tractor until niceguy updates his F350 as he stated he would in his support topic.
The script code for fixing the truck to pull FS13 trailers was posted in both this support topic and the F350 support topic.
Also, it will help us to help you, if you post log reports when claiming you are having issues with a mod. Update - I apologize guys, I uploaded the wrong version of the trailer. The fix was so minor I did not notice, and it works for people that have not corrupted their game with bad mods which is why it works for some and not others. I will ask Napalm to swap out the files as soon as I can. Sorry for the inconvenience.