Usually this error comes up because your IP address has been making too many requests, or you're trying to access GPS Visualizer with some sort of automated system. (Or, in the case of the "Quick Geocoder," I have to restrict access because Yahoo's service only allows my server a certain number of requests per day.)
If you want to rig up a legitimate service that works automatically with GPS Visualizer, please tell me what you're trying to accomplish, and I might be able to help. (Although if you need a geocoding API, it would be faster and more efficient to access Yahoo! or Google directly.)
If you need a very large batch of addresses converted, I can do it off-line (where it won't bog down gpsvisualizer.com) for an hourly fee; contact me for details.
