According to Mercedes-Benz S-Class owner's manual:
The Advanced Parking Guidance is switched off because the radar sensor system is temporarily inoperative due to electromagnetic interference near television and radio transmitter stations, toll stations, speed measuring systems, etc.
What is Parking Guidance?
The Parking Guidance system is part of the Parktronic system and helps the driver complete parallel parking when space is detected by the parking sensors mounted on the front and rear bumper.
If your Mercedes-Benz is equipped with a parking guidance system, it will have parking sensors mounted on the front and rear of the vehicle.
Over time these sensors may be covered by dirt or snow. Park the vehicle in a safe location and use a clean cloth to clean the area around the parking sensor.
Another widespread problem that triggers Parking Guidance Currently Unavailable warning message on a Mercedes-Benz is due to a weak main battery.
If your battery is not holding a charge, has recently died, or is not fully charged, it can trigger a Parking Guidance Currently Unavailable error.
Use a 12-volt battery charger to fully charge the battery, then test it to find out if the battery is good.
Another problem that can cause Parking Guidance Currently Unavailable See Oper. Manual warning on the dashboard is due to a faulty parking sensor.
Parking sensors can fail internally. If one of the sensors fails, the parking guidance system gets disabled even if the rest of the sensors are still functional.
The electrical connector at the back of the parking sensor can get damaged or suffer corrosion. You will need to remove the front and rear bumper covers to inspect each parking sensor connector.
Check to make sure that none of the connectors are loose or corroded.
In some cases, the wire harness for the parking sensors can be faulty, but that is unlikely unless the vehicle has been in an accident.
The parking sensor module itself can be faulty, even though these do not fail very often. If you can not communicate with the parking module, the problem can be due to another module being faulty or suffer water damage and therefore interfering with the communication of other modules.
If you notice Mercedes-Benz shows Parking Guidance Currently Unavailable See Oper. Manual on the instrument cluster, first inspects and clean with a clean cloth the front and rear parking sensors. Please turn off the ignition, wait a minute, and restart it.
If the problem persists, you will need to read the fault codes using a Mercedes-Benz scanner.