not a pdf or corrupted file

Thank you, your plugins “dk pdf” and “dk generator” are exactly what I need, but now I got a problem with “dk pdf” and wondered if you maybe could help, for I purchased your plugin “dk generator”.

The issue: First everything was fine, but suddenly an error appears when trying to open pdf after download: Acrobat says “could not open because it is either not a supported file type or because the file has been damaged.”
Strange is, that the pdf for other posts is working and also the first few tests with this custom post type was successfull.

I have the newest versions of “dk pdf” and wordpress installed and I allready tried to install older bersions of your plugin. It didn’t work as well.

Thanks and kind regards!

The page I need help with: [log in to see the link]