I see that the passes API breaks as latitudes approach 80 degrees. For example, if you try to see the upcoming passes over Spitsbergen via http://api.open-notify.org/iss-pass.json?lat=78.3187832&lon=16.0729979 you get the error "Internal Server Error, The server encountered an internal error and was unable to complete your request. Either the server is overloaded or there is an error in the application."
From an email: