The Country Code you have set on your AR750 does not work in Germany ie the AR750 is blocking the frequencies in use .
Go to Advanced UI (Luci)
Select:
Network
Wireless
Edit the wireless for the link to the hotel.
Select Advanced Settings
Set Country code to DE (Germany)
Click save and Apply.
This may also be in the standard UI, I don’t have access to one at the moment to check.