Hi,
it works now!!!
This was the tip that helped me:
Request the EPG for a channel (ZDF)
Now open this page on a separate page. (by clicking on the button at the bottom op the pop-up)
Because I couldn't find that button, I switched from new responsive design to the old "classic" design from Openwebif.
Now I could open the EPG-Data in a new window, and could find the url.
After that I testet Webgrab, and it worked!
meitevau