In the first half Frojdfeldt was good except for one moment when Carvalho deserved yellow. The first huge mistake was made by an assistant when he didn't signal that Drogba was offside and of course Drogba scored. After that the game was decided but Frojdfeldt made another two huge mistakes. In the 85th minute Alex pulled Larsen's shirt while he was in a goal chance , normally a red card but Frojdfeldt didn't think so. Also his second assistant didn't see anything. I really couldn't understand how they didn't see it because it was obvious form even from space. But that wasn't enough for Frojdfeldt so 3 minutes later he didn't award an also very obvious penalty for Chelsea after Drogba was fouled on. Frojdfeldt also made many other minor mistakes in comparison to this one. He is an experienced referee but he probably hasn't taken charge of enough qualifiers for Uefa Cup or CL.
The Schalke goalkeeper mad one big mistake and that was a goal for Chelsea. He allowed Malouda's shot to slip through his grasp and his legs. After that he made some excellent saves but all that didn't help Schalke to get a better result.