Try to change the ad type to a 468*60 instead of the link ads, you will notice the ads will change. this happened to me before. I just realized.
I tried this and it didn't make a difference. It still gives me the PHP/mySQL ads. And by the way, I did set the options to show public service ads when no others are available, so that's not the answer either. (At least I don't think those PHP ads are PSAs.) Thanks anyway. I appreciate the suggestion.
Sorry, I could not be of further assistance. That happened to me before as well. I just am not sure why it is happening to you.