Due to a large number of 'robots' that ignore the robots.txt and are not providing a proper contact address nor actually any identification at all, this check has been put into place to avoid these crawlers from taking away resources which could be used for real purposes, like serving human beings.
Information for automated queries
In case you want to automatically retrieve data from our site please contact us with details on what information is interresting for you and what could be a convenient format to receive that information in. It is quite likely that we can accomodate these requests if it can be made useful also to other people.
Under no circumstance automatically query these resources, we will ban on sight.