Can you please provide the actual Bing Maps API call without the key or provide the trace ID of the failing call? I am not familiar with "bing.com/rp". This looks like a network error and the call may not even be reaching bing with what I see above. Do you have a wireshark trace or similar?
Also, if you are using a Basic key, you may be hitting a usage limit if you are hammering the service. How many QPS (Queries per second) are you generating?