Hi Markus,
from what I can see, the final question mark is missing in the XML declaration.
Basically the first line should look similar to
<?xml version="1.0" encoding="UTF-8" standalone="no" ?>
There are thousands of websites that allow you to validate a XML file...for example this one.
I'm also attaching a sample DEDMAS IDoc XML file you can use as a reference...I hope this helps!
Best,
Riccardo