tokidoki

Hi everyone, I got into a Phd program, fall 2011. The project is funded by DOE and I accepted the offer. But on Apr 14, the Professor suddenly said that he had no available position in his lab and hoped my applications to other programs were fruitful. The school still admitted me, but without any kind of assistantship. He said the department will reconsider me an RA position in spring 2012. So I deferred my enrollment for one semester and decided to pay a visit to the school over this summer. But I have no idea what I should say to the professor when I meet him. I want to leave a good impression, but after all, this is like the most terrible experience I've ever had. Can anyone help me with that? Thanks very much!