What does BMW 528i code p0500 senor A means?

The P0500 code indicates a problems with the ABS system. If you have recently replaced wheel sensors, it sounds like one or more may be disconnected or flaky.

From datsc.com:
What does this mean? OBD Code P0500refers to
Basically this means that the vehicle's speed as read by the Vehicle Speed Sensor (VSS) is not working properly.
Symptoms Possible sumptoms of OBD code P0500
loss of anti-lock brakes the "anti-lock" or "brake" warning lamps on the dash may be lit the speedometer or odometer may not work properly (or at all) your vehicle's RPM limiter may be decreased the shifting of an automatic transmission may become erratic other symptoms may also be present
Causes Possible causes of OBD code P0500
A code P0500 may mean that one or more of the following has happened: The Vehicle Speed Sensor (VSS) is not reading (functioning) properly There is a broken/frayed wire leading to the vehicle speed sensor The vehicle's PCM is not correctly configured for the actual tire size on the vehicle
Possible Solutions The simplest thing to do is to reset the code and see if it comes back. Next, check all wiring and connectors that lead to the speed sensor. The location of the sensor depends on your vehicle. The sensor could be on the rear axle, transmission, or perhaps the wheel hub (brake) assembly. If the wiring and connectors are OK, then check the voltage at the speed sensor. Again, the exact procedure will depend on your make and model of vehicle. If everything looks OK, replace the sensor.