[Koha] Upload files in cataloguing

[Beda Szukics]

Hi all

I would like to upload a file and make it visible through the 856$u 
field. I followed the instructions on 
http://kohageek.blogspot.com/2015/12/attaching-files-to-catalog-records.html

The plugin appears and I can upload the file. But when I select the 
Choose (or Auswählen) buttom nothing happens. The same with the Download 
and the "Löschen" buttom. If I click on koha_upload I'm able to download 
(and maybe delete - I haven't checked) the file.

What is wrong?

Thank you

Beda