I can't say enough good things about Sun's work

Yesterday, Don sent a email to my managers, he said "I can't say enough good things about Sun's work". When I got the email, I felt so sad, I couldn't understand why he said that. I really didn't know what I did wrong. I still couldn't believe, so I asked Stephen what that meant. He said it meant excellent. I am relieved now, but I am still confused what I did so that he sent this email.