Umberto, can you help us please? i have tested my airports and all worked. today, without touching anything, EDDF is giving an odd mistake. It says sometimes that this door has a default jetway or no jetawa can operate at this position. Is really frustrating because when i designed it, it worked perfectly!
I checked your EDDF file, and the issue is that, at many parkings, you used short jetways with two tunnels. These cannot reach the door from the distance EDDF stands normally are in relationship to the parking position. That's depending on the airplane too, of course. I'm trying with the default 737.
So, either use longer jetways (at Gate A18, for example, switching from the 18/13 model to the 25/16 model fixed the problem) or, if you like the shorter jetways, use the 3-tunnel version instead.
Also, try to check pictures for the real world airport: I believe jetways at EDDF are more neutral grey (default) than the blueish grey (cool grey) you used, and they don't have the gate number over it.