Umberto,
Very friendly of you to reply, but as you can see in my reply to Kevin, I have already found a workaround:
Rename ft_jetwayLib.LOD.bgl > ft_jetwayLib.LOD.off. The manoeuvrable jetways don't show up.
Rename jets_static.bgl > jets_static.off. The static jetways dont show up.
Start P3D (P3D5.1 in my case)
Open GSX customize airport position.
Check the checkbox 'exclude jetway radius'. Neccessary in order to be able to select a new jetway later on.
Apply. Compiling is not desired.
Select all airport positions with jetways (77).
Select a new jetway, suitable for the EHAM bridges. No bridge (default).
Apply.
Quit GSX customize airport position.
Now I have replaced the default jetways at 77 airport positions by a new, better working SODE jetway. Unfortunately, I had to do this 5 times, because FlyTampa EHAM has 5 .BGL files (4 wind directions and 1 for all wind directions).
I understand that you would like to have more insight in my error message, but I hope you will understand that I will not change my customization again, now I have the situation that I was aiming at.