Trackback Ping Failure

I have my own blog software that I wrote and continue to improve as I go. Perhaps one day I’ll put it back on the market and see what happens. In the mean time, I’d like to be able to ping other sites but recently I’ve found that sending a trackback ping to many wordpress sites is impossible. All I get back is an error telling me I don’t have access, or that the ping is denied access for some reason. Any one know what this is all about?