Tsumego From Games 49

A problematic sequence - Moves 199+  

White plays to live and black responds with - logical so far, right? (Not saying that there's no better way - I'm too lazy to look that far back ;p) But something is definitely wrong with 3-6. White still can live after it with 7. (See #5765 at GP) Before I post it there - What's wrong with this sequence? (3-6) And what was the correct one? (Yeah I'm just too lazy to post it there now, so I thought I'll ask for your kind help with the vars. I did find something could be done otherwise there, It's not a blind shot - I just hope I was right.. ;)